Escherichia coli Type-1 topoisomerases: identification, mechanism, and role in recombination

This paper is a discussion of the biological function and properties of Escherichia coli topoisomerases. Five topics are considered. First, in the analysis of the electrophoretic mobility of negatively supercoiled topoisomers, we discovered that adjacent DNA bands on a gel need not differ by one in linking number. Second, we identified a new E. coli topoisomerase, topoisomerase III. Third, the mechanism of catenation of duplex DNA rings by E. coli topoisomerase I has been elucidated. Fourth, we describe the involvement of a type-1 topoisomerase, the resolvase of Tn3, in site-specific recombination. In catenation and recombination by type-1 topoisomerases, duplex DNA is topologically rearranged via the breakage and rejoining of DNA a single strand at a time. Fifth, we consider what cellular processes might be particularly suited for the involvement of type-1, but not type-2, topoisomerases. 47 references, 16 figures, 1 table