KOPS-guided DNA translocation by FtsK safeguards Escherichia coli chromosome segregation.

The septum-located DNA translocase, FtsK, acts to co-ordinate the late steps of Escherichia coli chromosome segregation with cell division. The FtsK gamma regulatory subdomain interacts with 8 bp KOPS DNA sequences, which are oriented from the replication origin to the terminus region (ter) in each arm of the chromosome. This interaction directs FtsK translocation towards ter where the final chromosome unlinking by decatenation and chromosome dimer resolution occurs. Chromosome dimer resolution requires FtsK translocation along DNA and its interaction with the XerCD recombinase bound to the recombination site, dif, located within ter. The frequency of chromosome dimer formation is approximately 15% per generation in wild-type cells. Here we characterize FtsK alleles that no longer recognize KOPS, yet are proficient for translocation and chromosome dimer resolution. Non-directed FtsK translocation leads to a small reduction in fitness in otherwise normal cell populations, as a consequence of approximately 70% of chromosome dimers being resolved to monomers. More serious consequences arise when chromosome dimer formation is increased, or their resolution efficiency is impaired because of defects in chromosome organization and processing. For example, when Cre-loxP recombination replaces XerCD-dif recombination in dimer resolution, when functional MukBEF is absent, or when replication terminates away from ter.