The lighthouse that guides DNA to its destination - Gradual distribution of an ATPase protein determines the destination of plasmid partitioning - Molecular Microbiology Article first published online: 6 OCT 2010. Niki Laboratory, Microbial Genetics Laboratory Partitioning of P1 plasmids by gradual distribution of the ATPase ParA Toshiyuki Hatano {Currently at: University of Massachusetts Medical School, Department of Cell Biology, Greenfield (Kip)Sluder lab} and Hironori Niki Molecular Microbiology , Article first published online: 6 : OCT 2010. 　DOI: 10.1111/j.1365-2958.2010.07398.x 　 Even in tiny bacteria with 2 micro meter size possesses system to segregate its chromosome or plasmid. We are researching partitioning of low copy number plasmids as the most simplified model system for DNA segregation. This low copy number plasmid are partitioned into daughter cells only by 3 essential elements, ATPase protein, centromere binding protein and centromere-like cis -sequence on plasmid. Especially for various role of ATPase are proposed to pull or push plasmids or guide plasmids as railway track for its polymerization into filaments. On the other hand, the how representative ATPase in plasmid partitioning, ParA drive plasmid partitioning thought Par A is reported to localize entirely in the cell without forming filamentous structure. Here, we first observed ParA protein periodically assemble and disassemble cluster at middle of living cell. 　 The position that ParA blinks changed from mid cell to cell quarter positions along long axis of the cell(red circle in Figure). Then replicated plasmids migrated toward and stayed at the points where ParA newly made cluster(Purple thread in Figure). When we observe carefully of distribution of ParA, ParA　gradually distributed of nucleoid structure of host cell without forming filaments. We propose a model that polymerization into filaments is not nesseary for plasmid partitioning but key is the periodical generation of gradual distribution ParA determines the direction and destination of plasmid (Figure). 　 ParA is distributed on the nucleoid and periodically clusters at mid/quarter cell positions. The focus of ParA-ATP (red region) at the midcell gradually shifts to the 1/4 position along long axis of the cell. Finally a new cluster of ParA is formed at the other cell quarter position prior to separation of the plasmids (purple). Following of ParA focus, one of the replicated paired plasmids migrates to the new ParA focus, while the other stays with the old focus. . ←Back