XerD unloads bacterial SMC complexes at the replication terminus

Bacillus subtilis structural maintenance of chromosomes (SMC) complexes are topologically loaded at centromeric sites adjacent to the replication origin by the partitioning protein ParB. These ring-shaped ATPases then translocate down the left and right chromosome arms while tethering them together. Here, we show that the site-specific recombinase XerD, which resolves chromosome dimers, is required to unload SMC tethers when they reach the terminus. We identify XerD-specific binding sites in the terminus region and show that they dictate the site of unloading in a manner that depends on XerD but not its catalytic residue, its partner protein XerC, or the recombination site dif. Finally, we provide evidence that ParB and XerD homologs perform similar functions in Staphylococcus aureus. Thus, two broadly conserved factors that act at the origin and terminus have second functions in loading and unloading SMC complexes that travel between them. [Display omitted] •Bacillus subtilis XerD binds novel sites in the replication terminus region•SMC complexes loaded at the origin are unloaded by XerD at the terminus•XerD functions as a site-specific unloader of translocating SMC complexes•ParB-mediated condensin loading and XerD-mediated condensin unloading are conserved SMC condensin complexes are loaded at replication origins by the partitioning protein ParB. Karaboja et al. show that condensins are unloaded when they reach the terminus by the recombinase XerD. Thus, broadly conserved factors that act at the origin and terminus load and unload SMC complexes that travel between them.