Identification of a unique domain essential for Escherichia coli DNA topoisomerase III-catalysed decatenation of replication intermediates.

A 17-amino-acid residue domain has been identified in Escherichia coli DNA topoisomerase III (Topo III) that is essential for Topo III-mediated resolution of DNA replication intermediates in vitro. Deletion of this domain reduced Topo III-catalysed resolution of DNA replication intermediates and decatenation of multiply linked plasmid DNA dimers by four orders of magnitude, whereas reducing Topo III-catalysed relaxation of negatively supercoiled DNA substrates only 20-fold. The presence of this domain has been detected in multiple plasmid-encoded topoisomerases, raising the possibility that these enzymes may also be decatenases.