Different localization of SeqA-bound nascent DNA clusters and MukF-MukE-MukB complex in Escherichia coli cells.

MukF, MukE and MukB proteins form a complex that may participate in the organization of folded sister chromosomes in Escherichia coli. We have found that a MukB-GFPuv4 fusion protein is observed as discrete fluorescent foci, which are localized within cellular spaces occupied by nucleoids, but not at the constriction site of cell division in living cells. In contrast, MukB-GFPuv4 is distributed throughout the whole cell when either MukF or MukE is absent. Statistical analysis revealed that most newborn cells have two foci of mukB-gfpUV4 at one-quarter and three-quarter positions in the cell length and one focus of SeqA-bound nascent DNA at or near the middle of the cell. Subsequently, the single SeqA focus divides into two foci, and then these migrate to the one-quarter and three-quarter positions. Before cell division, most long cells have two SeqA foci and four MukB-GFPuv4 foci. In early stationary phase, SeqA foci disappear, but one or two foci of MukB-GFPuv4 remain. We discuss the reorganization and proper arrangement of folded sister chromosome in the cell quarter positions, which are performed after release from the long-time cohesion of sister chromosomes.