Unlinking of replication catenanes in E. coli is largely achieved by a type II topoisomerase (TopoIV). However, the replication catenanes are also resolved by a site-specific recombinase (XerCD-dif recombination) without type II topoisomerase. In previous research we have characterized unlinking pathways under the assumption that iterative enzyme actions reduce the topological complexity stepwise. In this talk we focus on first steps of the unlinking pathways.