We have obtained many insights into the structural basis of ribosome function in protein synthesis from our structural studies of the 70S bacterial ribosome, and its complexes with substrates, protein factors or antibiotics. These have elucidated the mechanism by which this ribozyme catalyzes peptide bond formation. We have obtained the structure of the complex of the 70S ribosome with tRNAs and EF-G in a previously unseen compact conformation. This compact conformation of EF-G, unlike the elongated one, allows the simultaneous binding of a tRNA in the A site and EF-G. We propose that the conversion of the compact to the elongated conformations of EF-G is responsible for tRNA translocation. The structures of the 70S ribosome with the factor EF4 (LepA) with tRNA bound in the P site or in the A and P sites provide the first insights into EF4’s possible role in protein synthesis.