I'm Count Bernadette, Professor West, fellow Laureates, ladies and gentlemen. I feel very honored to be asked to come here, particularly

in connection with the sort of honor of having received a Nobel Prize. On the other hand, I must confess being slightly nervous speaking to a large audience. I think speaking to a large audience about something to whom one always has slight doubts as to its

ultimate importance. The Nobel Prize is always meant to signify something very great and outstanding. When one does science, one always has doubts, I think, as to what one does, particularly at a given moment as whether it will be relevant or not. I think I'm also apprehensive speaking to a large group,

maybe partly because of my training in Cambridge England. One always felt that one should understate a case, particularly if it's important. That is, if something is simple and important, you don't have to talk about it. On the other hand, it's clear that I have to speak today.

And I feel maybe perhaps at loss without my colleague, Francis Crick, with whom I worked on the structure of DNA. Unlike myself, Francis is rather exuberant. Those of you who have heard him will know that he is perhaps slightly un-English and liking to speak very loudly

about what he's done. And this might be illustrated by the fact that several years after Crick and I had done the work in Cambridge England, I had gone home to the States and then come back. And during the time at which I had been away from Cambridge England, the professor

of the Cavendish Laboratory in which we worked, the professorship had changed from Professor Sir Lawrence Bragg to the physicist Neville Mott. And Crick thought it appropriate that when I came back to the Cavendish that I should meet the new professor. So he went up to Mott and said that he'd like to have a meeting between Watson and the new professor.

And Mott is a, I guess you could say, a rather quiet physicist, a theoretical physicist with interests I'd say not very far outside of physics. Looks at Crick and said, isn't your name Watson Crick? Well, I think that indicated the, you could say,

maybe the interest of one physicist toward the field of, you could say, biology. That is complete lack of interest. On the other hand, that certainly has not been the, which you could say, I'd say the dominant theme. And in fact, the work which I will speak has,

in one sense, a rather strong connection with physics. This connection came back, arose, I think, rather gradually in the 1920s and 1930s when a number of physicists, particularly those who were interested in theory, thought that perhaps there

should be some very fundamental laws as the basis of living existence. And just as quantum mechanics, that way of thinking was revolutionizing both one way of looking at physics and then also of chemistry, that perhaps new laws would

be found which would really do something to make us understand biology. That is perhaps behind the existence of living material were some new laws of physics, perhaps, which physicists themselves had not understood.

This feeling, I think, was expounded on a number of occasions by Niels Bohr, who influenced the number of the younger physicists around him into thinking that perhaps the physicists had something to give biology. Now, among the students of Bohr, the most, I'd say,

important one was the young German physicist Max Delbruck, who worked for a period in Berlin with Lisa Meitner. And after that period came to the United States to learn some genetics. Because the physicists sort of reasoned

that the most important aspect of biology was perhaps the gene. That is, the gene was the sort of chromosomes were the most central thing, and that if you were to understand life, you would have to understand the gene. Now, at that time, one could say

there was sort of two ways, I guess, of approaching the problem. One was, I would say, we've seen from this distance now slightly mystical. That was that there would be something really different about living systems, which only the physicists could

find out. And this, of course, was a viewpoint which could hardly be accepted with ease by biologists because they were not physicists and therefore could never understand it. And the second view was more practical. That is, the living material was made up of something,

and you had to find out what it was. And that smelled suspiciously of chemistry. This is if one had to learn basically the chemistry of living material before you would find out what to do. So the physicists, I guess you could say, went in two directions in their interests. One was a slightly, I'd say, mystical, as we see it now,

who said there's something different. We don't know what it is, and therefore we will study genetics. The second was that, well, we don't know what else to do, so we'll try and find out what they're made of. And if we know what they're made of, then maybe the great insight will someday come.

If you, say, studied genetics, this was a rather uninteresting statement because biologists had been studying genetics and they could continue to study genetics. So just by saying this, the physicists, I say, made little impact.

The impact came, however, from a sort of general belief, I think, of people who were in physics that you should study the simplest of all possible systems if you're going to get anywhere. That is, that biology is the simplest, a very complex subject, and therefore you won't have the slightest chance of getting anywhere

unless you pick out the simplest of all forms of life to study. Now, this led by the sort of mid-1930s to the feeling that perhaps the thing, the sort of biological object upon which everyone should concentrate were the viruses because in some way they were thought to be living

and they were also known to be very small. That is, they were sort of thought to be the smallest object which you could study which had the property of being self-reproducing. That is, the property of going from one to two. And so the thought was that if you study viruses

and you ask how they go from one to two, you may really get at the heart of the matter of living material. And also, if you study viruses, almost directly you may find out what the genes and the chromosomes are because there was this suspicion that perhaps a virus was nothing but a naked gene.

This idea was expressed, I think, first in a very clean form by Herman Moller, the very great American geneticist who won the Nobel Prize, I believe, in 1945. Moller was fascinated by viruses for a very long time and said, well, study them.

But he never essentially followed, you could say, his own intuition that viruses were interesting and that he remained a sort of, you could say, an exponent of studying the fruit fly, Drosophila, which probably Moller's own real intelligence would tell him would lead nowhere, which it did. That is, the study of Drosophila as such

never gave us real insight into the nature of the gene that is following its first very wonderful period. Instead, our insight has come as, the physicists really, I think, predicted from a study of the simpler systems, in particular from a study of the viruses.

Now, of the viruses, there have been two main classes which I think have affected our thought. Well, there have been three, I guess you could say. One were the viruses which multiply in animal cells and they've interested us chiefly because they cause disease which affect us. And the second have been a series of viruses

which have multiplied in plants and which have had a very great impact on science because they were the first viruses to be studied chemically in a very clean fashion. They were the first viruses that people realized were simple and this was, I think, expressed by the idea that perhaps they were nothing but molecules.

And the awarding of the Nobel Prize to Wendell Stanley for his discovery that tobacco mosaic virus particles could be purified and form crystalline-like aggregates expressed, I think, everyone's deep, the deep impact of the discovery that perhaps a virus could be studied as a chemical object.

And Stanley's original work with tobacco mosaic virus has been followed up in a number of laboratories of whom certainly one of the most important is that of Professor Schramm in Tübingen. And this led to, I guess, could say maybe two principles. One, that they were simple

and second, that the most important part of the virus was the nucleic acid. That is, the viruses when you studied them chemically were found to consist of a protein proportion and a nucleic acid portion, but the thought was that the genetic component was the nucleic acid portion.

And if one asked, well, why did they work on the plant virus? So this is really a simple fact that you could isolate from plants very, very large amounts and so you could do chemistry on them. That is, you could do chemistry on them in the 1930s when you require large amounts of the material. On the other hand, for everyone,

you could say except a botanist, plants are rather difficult to work with. That is, you, say, get one cycle of tobacco plants a year and you sort of have to think in year-long cycles. That is, it's a rather slow thing to work with. And I guess I must confess belonging to a sort of group of biologists who regarded that plants

were really too uninteresting to work with. It'd be sound prejudice, but from the viewpoint of the geneticist, if you get just one cycle of plant a year, it's rather dull. The system which instead really has dominated things from the biological viewpoint have been viruses which multiplied in bacteria.

This was the system which the physicist, Delbruck, decided would be the most interesting to work on. And so in the late 1930s at the California Institute of Technology, he began studying in a very sort of simple fashion, well, what could he find out about the multiplication of a virus? This work which started 30 years ago

has now multiplied many fold and there are many hundreds of people now working in this area. And I'm sort of particularly connected with this because it was my sort of first introduction to science some 20 years ago when I started working with Delbruck's friend, the Italian microbiologist, Luria.

And then when the sort of feelings were just largely of hope. Which is you study the virus and you count how they go from one to many and maybe this will give you great insight as to what happens. Now, there was just one problem with, you could say, the whole business that is you,

you said you want to study something fundamental which is the multiplication of a virus and you think maybe the virus is something like a gene and you count it going from one to many and you want to get some fundamental insight. And in the minds of at least a few of the people, maybe there's the feeling that you only understand

the real insight behind this process by understanding or developing some really new laws of physics. Now, the thing with sense they always sort of stuck in our throat was that you didn't know what you were talking about. That is you had the word virus and then you could simplify it by saying

that just like tobacco mosaic virus was protein and nucleic acid, the bacterial virus had two parts, the protein component and the nucleic acid component. And here the guess was that just like with the plant virus one should concentrate on the nucleic acid. And so you would ask, well, how do you go from one nucleic acid molecule to many?

Or one to two, that was the real process. And here you really felt maybe that if you were very clever you could guess the whole thing. Or I guess in my own particular case what you tried to do was you said, well, you really can't define the problem until you know what the nucleic acid is.

So that means finding out what DNA is. And it was at this stage that I feel you could say a brief period abandoned any interest in bacterial viruses and went to Cambridge, England with the thought that perhaps there with the sort of advanced techniques in x-ray crystallography one could find out what it was.

And I won't talk today about that sort of work because I imagine that virtually everyone here has at least read of this story on one occasion or another. But the answer which came out, that is that the structure of DNA, which we guessed was the fundamental genetic material,

was a complementary double helix in which if you knew the structure of one chain you knew the other, was, well, I guess you could say it was a very, very pleasant shock. You could say, well, we don't have any ideas, so we'll study its structure. And we'll be slightly afraid that we will find the structure and then it will be dull

and someone else will have to work very hard to find out what it means. But when we found the structure of DNA, we knew that there would be, you could say if there was ever a case where understatement would do the job, it was DNA, that is.

The structure was so interesting that I guess our only fear was not that it would be unimportant, but that conceivably in some way that we could fool everyone by proposing something which was wrong. That is, if it was right, it had to be important. If it was wrong, it would be a tremendous folly to have sort of raised everyone's hopes

that this was the answer to everything. But fortunately it was right. That is, when we saw the double helix sort of reactions of people vary, but generally everyone said it was very pretty, so pretty that it had to be right. And it was right.

Now, this was important, I guess, not only because it was right, but because you could say it simplified the problem enormously. When I was sort of in school and didn't know what life was and used to read rather horrid biology books which would have opened with one or two pages

description of what living material was, which it moved or it got irritated or something like that, that one always felt there was something else. And as a boy, one had always been told that, as well say, complicated physics was so complicated that it could only be understood by very few people.

The sort of example which was always thrown at us was the theory of relativity, which was a very profound idea and very difficult idea. In one word that perhaps biology would be the same way, that is, really understand biology, take a very, very sophisticated mind who would finally master it

and then have great difficulty communicating it to someone else. The truth, however, is just the opposite. That is, the fundamental sort of basis of the self-replication is so simple that it can be taught to very young people and, in fact, now is. So the sort of whole theoretical basis, I think, of which one now develops biology,

we now know to be very simple, because the ideas are simple chemical ideas which can be communicated easily, which is fortunate because, whereas I will say, to start with, the fundamental genetic principles are simple, one would be very naive if one said that

it would be easy to solve many biological problems. But one can at least start with the fact that the theory is simple and there will be enormous complexity to find out, but that if you don't get too confused to start with, that one may have a chance at really solving more complicated problems. Now, today I want to talk about a bacterial virus

which is a very simple virus, that is the simplest virus we know about. And the reason we study it is just this fact, that this is the simplest, and we want to understand completely how a virus multiplies. In this sense, one should understand

that a virus is more complicated than a gene, and maybe, let's see, I'll use the book, can you hear me here? Yes. Well, why not to summarize the sort of very, very large sort of collection of facts.

We now know that the gene is a DNA molecule, which we know now to be a double helix. Now, in fact, I said the gene is, but that should be slightly inexact, I should say, at least some chromosome type.

And I'll speak here of the bacterial chromosome, which we know to be a single DNA molecule. Now, the relationship between DNA molecule and gene is that you can subdivide this DNA molecule, which goes on and on and on,

into a number of segments, which we can call a gene. Now, each of these genes is responsible for the sequence of amino acids in a protein,

so DNA being a sort of linear sequence of nucleotides determines a linear sequence of amino acids in proteins. So that's the cycle, and you could say, to use a phrase quite old,

one gene determines one protein. This was something that geneticists thought, that there was a nice, simple relationship. And they said this before one realized this sort of great, simplified fact, that the gene was a linear collection of nucleotides,

and the proteins were a linear collection of amino acids. So it was one linear sequence determining another linear sequence. Here, one should have an idea of the, so you could say the complexity of the organisms we're dealing with.

The bacterial viruses, which virtually everyone has studied, multiply in a bacteria called Escherichia coli. Now, this is a relatively simple bacteria. Looks like a rod, this is a rod shape, and it's, say, two to three microns.

In this direction, it's about one micron. In this, the chromosome is a single DNA molecule, which is a, this is our bacteria. The chromosome, and I'll simplify here,

is a single circular DNA molecule. And from the chemist's viewpoint, if you want to indicate how complex it is, the DNA has a molecular weight of two times 10 to the ninth. Certainly the largest molecule, which I'm not going to discuss.

So the basis of it is a very large molecule. Now, this is divided into probably about 3,000 genes. We don't know the exact number, but it's certainly not less than 2,000 and probably not more than 5,000. But the number of genes which one has is this number.

Now, depending on your viewpoint, this can either be very simple or very complex. And I would say biochemistry has progressed to the viewpoint that 2,000 seems simple. That is, it's a number which doesn't overwhelm us

and send us out of science. It still keeps us within science. So you could say that if you could completely understand the bacteria, if you would know each, the function of each of these genes. That's sort of the level of what we're trying to understand. Now, this is not the smallest bacteria. Perhaps there are bacteria which are two

to three times simpler. That is, which would have maybe one third of the genetic material. But by accident, the bacteria which everyone has concentrated on has about this amount of DNA. If we'd started over, we might have picked a slightly simpler one. But it wouldn't have changed matters very much. Given this picture, one can say,

well, what is the relationship now between the chromosome and the virus? Now, a virus is best looked at as a sort of small chromosome. That is, a small piece of nucleic acid which is surrounded by a sort of protein shell.

We now realize that whereas 30 years ago one might have sort of said that a virus was perhaps a single gene surrounded by protein. We now know that it's best to say that a virus is a small chromosome surrounded by protein.

And it has the essential ability that when you put this, you could say viral chromosome, if it gets into a cell, this chromosome will then multiply. We multiply album control and form large numbers of new copies and then be surrounded by new protein cells.

Now, here you can ask how many, really how complex is the viral chromosome? That is how really big it is. Now, by accident, the viruses which were studied by Delbrook, T2, T4, we now know to be relatively complex viruses.

And they contain probably around 200 genes within the viral chromosome. So this is a fairly complicated option. And if you're going to completely describe a virus like this, one would have to take this chromosome

and say what each of these sections did. So if your aim was sort of complete chemical description, you would say that this is a little too complicated. And if you wanted to find the virus which you could say describe as well as you can describe a Swiss watch, that is every component,

so you knew exactly how it worked. And if you wanted to describe the location of every atom, you wouldn't work with this, but you would work with something small. So you would search for a smaller virus. In fact, there are a number of much smaller viruses. But there's sort of one further complication

that one should make. That is up to now I've said either nucleic acid or DNA. And the cycle which we now know is as important as we could say that you start out with DNA, and then it determines protein. And in between is an intermediate

that you make a second form in the quic acid, right in the quic acid, which then serves as the template for protein. This sounds sort of unnecessarily complex, but you could say this is the way it is, and we now know the essential components of this story pretty well. Now the key to the whole thing was that DNA,

you could say was self duplicating. And the fundamental biological, sort of the fundamental chemical basis of this self duplication was base pairing. This is the ability to form a complementary double helix

with the base adenine pairing with thymine, and the base guanine with cyclosine. This is the sort of basic principle behind self replication.

The adenine, thymine, guanine, and cyclosine. Now this would be a sort of complete picture if it were not for the fact that some viruses, and you could say the most important was tobacco mosaic virus, the virus studied in great detail by Professor Tran, this group,

called TMD, doesn't contain any DNA. And this was an embarrassing fact because if you said, well DNA was the gene, and you needed genes wherever you had life, then you were faced with the fact that this virus didn't contain any, but that it instead contained RNA.

And so RNA also must be a genetic material. And this means that you must also have a cycle, well, which goes this way. That is RNA must in some way be able to self replicate itself, and then this RNA must somehow determine protein. So you must have two different sort of cycles

of the transferred genetic information. One which is based on DNA, and the other which is based on RNA. Now, here one can ask, well, is this cycle here really the same as the cycle by which DNA went around?

Are these based on the same principle? And here, the first fact which one can really say is that chemically, RNA is very similar to DNA. And you can go further and say that if you took RNA chains, you could form a double helix just like DNA. So you could theoretically imagine

the replication scheme for RNA which was the same as DNA. The question however was not could it exist, but in fact, is this the system? Now, over the past really five years, this problem has been investigated in very great detail. And it's been investigated in detail largely

with a group of bacterial viruses, that is viruses which multiply on the same E. coli. But these are bacterial viruses which unlike T2, which are DNA viruses, there's a group which contain RNA.

These are bacterial viruses and they have different names. The first one which was discovered is called F2. In my laboratory, we work with a very similar one called R17 and two begin, they work with one which is called FR. They're all very similar viruses. And they have two, you'd say,

well, what's the real interest? Why focus attention? The first reason is that they contain RNA and you want to learn more about RNA. The second reason, and they contain RNA and they multiply on E. coli. And multiplying on E. coli is very important because it takes just 20 minutes

for the bacteria to multiply. You have an enormous knowledge of the genetics and so it's easier by several orders of magnitude to work with E. coli than to work with any other form of cell if you want to obtain precise chemical answers. So just the fact that this existed would mean that a large number of people would work on it.

But even more interesting was that this group of viruses is chemically very simple and they're very small. This is the total molecular weight. There's only three million. Whereas if one would look at T2, the molecular weight there was two times 10 to the eighth.

So here we have a very simple virus. It's simple and it's made up of a single nucleic acid chain with a molecular weight of 10 to the sixth. Now here one should make a fundamental distinction between this type of virus and the T2 one

which you could say is made up of DNA which is double helical. This virus is made up of just one strand of nucleic acid. And there's not two strands twisted around each other but just one strand. It's single stranded in contrast to being double stranded. And it contains just 3,000 nucleic acids.

Now the question we sort of pose ourselves, can we completely describe how this virus multiplies? It's the simplest virus we know. That is if I wanted it's simplest and one that has the shortest nucleic acid chain and say if one wants to compare it

to tobacco mosaic virus, tobacco mosaic virus has a nucleic acid chain which is twice as long. So in this sense it has one half the genetic information and so it should be easier to study. We just have a couple slides there. Now here's the sort of cycle which everyone now knows about DNA

serving as a template for RNA and then RNA making protein with DNA being self replicated. This is the normal transfer of genetic information within cell. Now the second form of cycle which exists is if you start out with RNA and RNA then the genetic message

and RNA can be translated into protein but you have this cycle here. We want to study how this happens. Now this is the transfer of genetic information following infection of a cell by an RNA virus and up to now one can say that as far as we know this cycle exists only following infection

of a cell by a virus. There's no evidence of it occurring without viruses though this rule may be broken. One doesn't know whether this will in fact always be the case but it's the only cases which we now can study. Now in this next slide

there's a sort of summary of all the biochemical events in going from say DNA finally to a polypeptide chain and I won't go into this in any detail because Professor Lippmann will speak about protein synthesis in detail two days from now. But the main sort of point here is that

you have three forms of RNA which one is the genetic message and that the proteins are synthesized on sort of small bodies called ribosomes and that as the protein is synthesized the sort of genetic message moves across the surface of a ribosome and as it moves across

the polypeptide chains are elongated. And one should say one other fact that the sort of precursor for protein synthesis is an amino acid attached to a molecule which is called Sogibor. Now in the next slide is an electron micrograph of a ribosome.

Now the ribosomes are the small particles or the sort of factories for making proteins and this electron micrograph was taken about six years ago and unfortunately one must say that since then no one has taken a better one. Our detail is still fragmented. These are particles which are about 200 angstroms in diameter

and the particles have molecular weight of about three million and they're made of two subunits. There's a small one and a large one and in the next slide there's a sort of very diagrammatic view of these which just says there are the two subunits and that the subunits are made up of a large number of different proteins.

The structure of a ribosome is very, very complex and we're nowhere close to finding that. Now in the next slide is again a sort of summary of the fact that when a polypeptide chain is grown that the precursor is the amino acid attached to this small type of RNA.

One should just sort of set one fact, is that whereas all DNA is thought to be genetic, that is all the DNA in a cell essentially codes for amino acid sequences, that RNA, there are three types of RNA of which only one type carries the genetic information.

The type here which is attached to the amino acid, this is not genetic RNA but that one should just remember that the growing chain is attached to it. In the next slide is just sort of a very schematic event of what happens in protein synthesis

that you have a growing polypeptide chain sort of attached to a ribosome via its mRNA molecule and then a new amino acid comes in and that you form a peptide bond. These details are basically unimportant to what I'm gonna talk about so I won't go into them now.

Now in the next slide here we'll go over to the RNA virus which I want to talk about. This is R17 which as I've said is very similar to several other small RNA proteins. Now as far as its structure, you can say well we want to find out

how it multiplies and it's the simplest of all viruses that we know anything about. Now how simple is it? Well first of all in the center of the virus is an RNA molecule which consists of a single chain which contains 3,000 nucleotides. Now this fact immediately tells us something.

It tells us that the amount of genetic information here can essentially order 1,000 amino acids because what we know of the genetic code is that successive groups of three nucleotides sort of determine a single amino acid.

So if you have an RNA message which contains 3,000 nucleotides, you can order essentially 1,000 amino acids by it. So we know essentially the limit. Now essentially what is necessary for this? Well what else is the virus? The virus in addition consists of two sorts of protein molecules.

Now one of the protein molecules we call the co-protein because it's present in the largest amount and there are 180 copies of this protein in every virus part. And the molecular weight of the protein is 14,700 and contains 129 amino acids

and the complete sequence of this has been determined. Now in addition to this protein which makes up about almost 99% of the total protein of the virus, there's a second protein which we think is given different names. We call it the attachment protein and the evidence which we have now suggested

probably there's only one copy of this protein per virus particle and we know its molecular weight is about 35,000 and it contains 300 amino acids. And we're now trying to study this protein in detail but it'll probably be several years before we can get enough of it to do an amino acid sequence.

So it's not very easy to isolate. In fact it's quite hard to isolate. So if you could say well what must you do when you make a new virus particle? Well you've got to make new copies of the co-protein, you're going to have to make new copies of this attachment protein and you're going to have to make new RNA.

So you have three things to make when the virus particle replicates. Now in the next slide you say well what is the life cycle of the virus? These viruses have a sort of peculiar sort of life cycle in that they all multiply only on male bacteria which is the E. coli.

There are two sexes, the male and the female and the male bacteria have small very thin film that's coming out from them which are called pili and the virus particles attach to this. This is the sort of first step in the multiplication of the virus.

And what was within a minute or so after the virus attaches to this pili then the nucleic acid somehow has got inside bacteria. Now we don't know how you go from here to here that is but in the next slide one puts it sort of diagrammatically

we think well in fact one knows that this filament is howl and in some way we think the nucleic acid moves down through this narrow channel into bacteria. Now we can't be more precise because we know nothing about the structure of these thin filaments

and it's an obvious thing for someone to do to find out their structure. However there are only a very very small percentage there are only somewhere on the average between one and three of these per bacteria there are only about 100 angstroms thick and so chemically they will be rather hard to isolate in large amounts.

So we're starting to do this. Well this is probably you could say the first step. Now in the next slide the sort of in a very diagrammatic way illustrates what must happen. The first within a sort of minute after the absorption of the virus to the pili nucleic acid is in

by about 15 minutes inside the bacteria you can see some completed new virus particles appearing and by about 35 minutes after the cycle starts holes develop in the wall of bacteria and these newly formed virus particles leave the cell.

Now the number of virus particles which grow or appear within the cell is it can be up to about 20,000 particles per cell. So you go from about one to 20,000 and this can occur in about 30 minutes. In fact it becomes so tightly packed that you can't see actual three dimensional crystals

of the virus particle forming in the cell just before it breaks open. So you could say that at the final stage maybe 10% of the mass of the bacteria has become transformed into virus particles. So it's extraordinarily efficient process. If one wants to analyze this in more detail

you can essentially measure three things. First you can measure the appearance of new molecules of the coat protein. You can measure the appearance of the attachment protein. And there's a third protein which is involved and that is that it's been discovered that in order for the RNA to replicate

that has to go from one RNA molecule to several there's a new enzyme which appears in the cell which is given several names but I'll give it the name replicase. This is a specific enzyme which is not present in uninfected cells but which appears

after virus infection and this enzyme is responsible for RNA replication. The reason you could say that RNA doesn't self-replicate in normal cells is this enzyme is not present and as we shall see in a moment this enzyme is coded for by the genetic material

of the virus that is the RNA strand carries the genetic information to make this enzyme which causes RNA self-replication. Now in the next slide if you can sort of study the kinetics in an infected cell of the appearance of you could say these three proteins

which are necessary for making the virus. One, the coat protein and this is made in large amounts for a long time and the second two proteins are this attachment protein and then the enzyme RNA replicates the enzyme which is necessary for the self-replication of the RNA.

Now one sort of interesting fact here is you'll notice that you make the coat protein for a long period of time and you make very many copies of it whereas you make many fewer copies of the replicase and the attachment protein and also their synthesis stops rather early. You make them for a short period of time and then you stop.

You could say well this makes biological sense to stop making attachment protein early because you need only very few copies of it. You don't want to make a large amount of it and it would be very silly to make equal copies when your virus particle only needs a small number. Now here you could say this is an example of a control mechanism making more one protein

than another what is its molecular basis. Is essentially here a structure which shows the viral nucleic acid which is our one chain here and this shows it soon after it enters the cell and after it enters the cell the ribosomes attach at one end

and they move along the RNA molecule and as they move along the protein which is being made comes up. This is coat protein which is being made and one can see now that there are essentially three genes here in the virus particle. All our evidence says that there are just three and we have identified each of them.

The first is the coat protein which seems to be the first and then the attachment protein comes second and then the replicase comes third. And the relative sizes we don't know exactly but this would be smaller because this has to decode for only 129 amino acids. This isn't really drawn to scale.

This one here has to code for about 300 and this one probably has to code for about five. This adds up about to the thousand amino acids that we expected. Now you could say are we absolutely sure and the answer is no. If there was a very small protein between here and here we might not have discovered it yet

but conceivably we now know each of the three. In this process you could say that we have an RNA molecule, the chromosome which codes for pre-genes and that at the beginning here there must probably be a start. Well you could say here as you're going along there has to be a signal which says stop

and then you might guess also that there's a signal which says stop. So I put here just start and stop and there should be a stop here. Start, stop, stop. We now have some information on what the starts and stops are. So yes, okay I have to say two things.

You might have thought that the chain would start with a, that the first sort of sequence of nucleotides would be a start signal and the last would be a stop signal. But in fact it looks like that the virus chromosome is more complicated in that you have some nucleotides

which are not the start signal. You go along some nucleotides and then you get a start signal and at the end you have a stop signal and then you have another series of nucleotides which must do something that we don't know yet. Now in the next slide shows probably the central principle for the general problem.

How do you make more of one protein than another? That is why do you make a large number of co-protein molecules and only a small number of the attachment protein from the rupture place? The reason is that after you make a co-protein and it's completed and it folds up into its right three-dimensional form,

then these molecules have the specificity so that they go and sit on the RNA chain and block the ribosome from moving on. There seems now little doubt that this is, really happens and so as soon as you've made a small number, so the equilibrium will say that some will be sitting here

and the ribosome can't go on. And it seems probably now likely that the ribosome only attaches at the end of the molecule and then moves across. So if in some way you block it, you will make more of the first than of the second. Now in the next slide, well here, I just want to state the facts here

that in the genetic code we know that it's groups of three nucleotides which determine given amino acids and that the start codons may be AUG and GUG. And essentially they code for an unusual and amino acid called formomethionine and I simplify it here, which I'm cheating slightly

but just to point out that there are start things, it's more complicated. Now as far as stop, we know that these will all cause stopping but we don't know how this is done. Now this was a funny story which came out, first really studying this virus was that you start at least the making

of all proteins in E. coli by putting in this amino acid called formomethionine which is just the amino acid methionine with a formal group attached to it by the amino end. Now this was a funny fact because when people had isolated proteins from the bacteria, they had never seen this before.

In fact, this led to the discovery of the cycle shown in the next slide in which you start, this shows you the beginning amino acid sequence for the code protein which goes formomethionine, alanine, serine, asparagine, threonine, phenylalanine. Then after you've made this, there's a specific enzyme which we've isolated

and deformulase which removes the formal group and then there's a second enzyme which takes off the methionine and this gives you the sequence which you find inside the cell in the intact virus pump. This is a sort of, you could say, level of complexity which a theoretician would never guess.

We know this is a cycle which happens and no one can say why it happens. This is what the advantage of the cell of having this cycle. We know that you always start this way, you end up this way. This is a sort of general rule, I guess, that biochemists never guess what's going to happen. This is you find out what happens

and you try and find the reason afterwards. Whereas one can say theory helps you, it helps you in a few cases, but in most of the cases, you just find out what's up just by doing experiments. Now, this is, you could say, the general picture for making the protein. One RNA chain which codes for three proteins

with start and stop signals and with something funny at the two ends which we don't understand. Now, I'd like to sort of conclude with saying that with the last factors, you could say, well, we have an enzyme which makes RNA and now how does this enzyme work? This is, do you use the principle of base pairing

or is there some other completely different cycle? In the next slide, shows how this enzyme works. The enzyme works as we start out with a single chain here and then the enzyme makes a complement and the principle which you use in making this complement is base pairing.

This is the same principle which is involved in DNA replication is involved in the replication of RNA. In RNA, you don't have the base finding, but you have yourself, which the viewpoint of the base pairing rules is identical, so I won't bother you with that, but to say that in the replication of RNA, you go through a double helical intermediate

and so you end up with a, in the middle of the replication, you end up with a double helical RNA molecule and we should say that the strand which we start with, we call the plus strand and its complement, we call the minus strand, so the enzyme has moved along here,

you could say, from right to left. Now, what we want to make, however, is not new minus strands. The virus particles contain only plus strands. That is, you don't find a mixture of the two in the virus particle. You only find the one sequence, the plus strand. Now, in the last slide,

we see here the second stage in the replication of the RNA, which is that given the replicative form, the enzyme now moves in the opposite direction and makes a new plus strand and then we end up with free enzyme and this enzyme will again go over and sit here and make new plus strands.

Now, one can then conclude, I think, by saying that we probably understand all the essential steps in the multiplication of the simplest virus we know about. We understand both, how it makes the protein, which is involved, and the way it makes protein

in the case of the virus is just to use exactly the same machinery for making protein, as you find in the normal DNA-RNA protein cycle. It's exactly the same system. Nothing is different. The virus essentially uses the same system. The replication of the RNA, you use basically the same principle

as you use in DNA-based pairing, but you have to have a specific enzyme which doesn't exist in uninfected cells, which essentially lets an RNA chain make its complement. This is a very specific enzyme and its specificity is limited to that of the specific virus.

Now, we can't say in detail, you could say this enzyme, if you look at it, in slight complication, is more complicated than you might guess because the enzyme can make both plus and minus strands. It can move from right to left or from left to right, which, when you think of it from a chemical viewpoint, means it's quite an interesting enzyme

and so far we cannot say anything about how this happens. No one has yet isolated the enzyme determined. Well, the enzyme has been isolated and you can make infectious RNA and the test tube was first done in Spiegelman's lab, which was a very important discovery because it showed you could really do everything in the test tube.

But we haven't gone to, you could say, the second stage of really isolating the protein, determining its three-dimensional structure and then saying how it can go both from right to left. These things really await the future. Now, you could say, where do we go from here? Well, I think one can say that the sort of,

the chief conclusion is that the viruses, I say, are no longer a very mysterious thing. That is, we now see their relationship to the normal cell cycle and we see the relationship now for both viruses which contain DNA and RNA. And we could also say that we now probably have the confidence

that if we have a simple enough virus, we probably will be able to understand all the steps of its replication, at least if we have a simple system to work with. That is, as long as we're dealing with a virus which contains only a few genes, it should be possible to understand the virus

almost as well as you understand the Swiss watch. It has all its components. Now, you can say, why should you, is it worth the effort? Here, I guess it's partly a matter of one's own interest. That is, how deep do you actually want to understand it? That is, there's a sequence of 3,000 nucleotides.

Should anyone go through the trouble of determining the exact sequence? I think probably yes would be my answer, even though right now it sounds like an impossible task, which is to do a sequence of 3,000 nucleotides. But 10 years ago, one would have said doing a sequence of 100 is an impossible task, and it's been done in the case of soluble RNA.

And so with sort of basic improvement of chemical techniques, it probably will be possible, I'd say, someday to do the complete sequence. Then you could say we know everything we want to about the virus. So you want to do it just because if you do the complete sequence, you'll see the start signals, you'll see the stop signals,

you'll find out more about the genetic code in great detail. Now, I think there's an extension of this, though, which you could say maybe in medical directions, you could say that, well, we're interested, or everything I've talked about now has been viewing the virus as something which a pure scientist wants to find out about.

I think there's also, you could say, the medical question that viruses are interested. We're interested in viruses because they cause disease, and we may find out something about fighting them if we know their structure in complete detail. And from my own viewpoint, one of the most, I'd say, interesting things

is that a number of the viruses which are able to cause cancer are very small viruses. That is, they're not big ones. In particular, there's a virus called polyoma, which is a DNA-containing virus. It's a circular DNA molecule which probably contains genetic information

for only, at most, six to seven genes. And this is a virus which multiplies in mice, and it's much harder to work with bacteria. You could say that if you move from a bacterial virus to an animal virus, maybe your level of complexity moves up a hundredfold, harder, harder to work with.

But that sort of being optimistic that you could say every 10 years you can work with something an order of magnitude more difficult, and also saying there's some people who are more clever than others, that maybe within the next 10 years one can take a virus of this sort of complexity, of multiplying an animal's cells,

and completely define what all its genetic information does. And if you know what all its genetic information does, then maybe one is much closer to understanding why, say, this virus can cause a tumor. And I feel quite sure that maybe within 10, and certainly within 20 years, someone will be able, say, to get on this,

and arrest them, and take a virus like this, and say what it does and why it causes a cancer, which I think will be a great achievement when it happens, so thank you.