Initiation of chromosome segregation in bacteria is achieved by proteins acting near the origin of replication. Here, we report that the precise choreography of the terminus region of the Escherichia coli chromosome is also tightly controlled. The segregation of the terminus (Ter) macrodomain (MD) involves the structuring factor MatP. We characterized that migration of the Ter MD from the new pole to mid-cell and its subsequent persistent localization at mid-cell relies on several processes. First, the replication of the Ter DNA is concomitant with its recruitment from the new pole to mid-cell in a sequential order correlated with the position on the genetic map. Second, using a strain carrying a linear chromosome with the Ter MD split in two parts, we show that replisomes are repositioned at mid-cell when replication of the Ter occurs. Third, we demonstrate that anchoring the Ter MD at midcell depends on the specific interaction of MatP with the division apparatus-associated protein ZapB. Our results reveal how segregation of the Ter MD is integrated in the cell-cycle control.

The organization of the Escherichia coli chromosome into a ring composed of four macrodomains and two less-structured regions influences the segregation of sister chromatids and the mobility of chromosomal DNA. The structuring of the terminus region (Ter) into a macrodomain relies on the interaction of the protein MatP with a 13-bp target called matS repeated 23 times in the 800-kb-long domain. Here, by using a new method that allows the transposition of any chromosomal segment at a defined position on the genetic map, we reveal a site-specific system that restricts to the Ter region a constraining process that reduces DNA mobility and delays loci segregation. Remarkably, the constraining process is regulated during the cell cycle and occurs only when the Ter MD is associated with the division machinery at mid-cell. The change of DNA properties does not rely on the presence of a trans-acting mechanism but rather involves a cis-effect acting at a long distance from the Ter region. Two specific 12-bp sequences located in the flanking Left and Right macrodomains and a newly identified protein designated YfbV conserved with MatP through evolution are required to impede the spreading of the constraining process to the rest of the chromosome. Our results unravel a site-specific system required to restrict to the Ter region the consequences of anchoring the Ter MD to the division machinery.