Coordinating DNA replication with cell division: lessons from outgrowing spores.
Progress in solving the long-standing puzzle of how a cell coordinates chromosome replication with cell division is significantly aided by the use of synchronous cell populations. Currently three systems are employed for obtaining such populations: the Escherichia coli 'baby machine', the developmentally-controlled cell cycle of Caulobacter crescentus, and Bacillus subtilis germinated and outgrowing spores. This review examines our current understanding of the relationship between replication and division and how the use of B. subtilis outgrowing spores and, more recently its combination with immunofluorescence microscopy, has contributed significantly to this important area of biology. About 20 years ago, and also more recently, this system was used to show convincingly that termination of DNA replication is not essential for a central septum to form, raising the possibility that the early stages of division occur well before termination. It has also been demonstrated that there is no major synthesis of the division initiation proteins, FtsZ and DivIB, linked to initiation, progression or completion of the first round of chromosome replication accompanying spore outgrowth. This has led to the suggestion that the primary link between chromosome replication and cell division at midcell is not likely to occur through a control over the levels of these proteins. Very recent work has employed a combination of the use of B. subtilis outgrowing spores with immunofluorescence microscopy to investigate the relationship between midcell Z ring assembly and the round of chromosome replication linked to it. The results of this work suggest a role for initiation and progression into the round of replication in blocking midcell Z ring formation until the round is complete or almost complete, thereby ensuring that cell division occurs between two equally-partitioned chromosomes.
Department of Biochemistry, University of, NSW 2006, Sydney, Australia. L.Harry@biochem.usyd.edu.au
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D001412:Bacillus subtilis / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002455:Cell Division; D002876:Chromosomes, Bacterial / Q000378:metabolism*; D003598:Cytoskeletal Proteins; D004261:DNA Replication; D008954:Models, Biological; D013171:Spores, Bacterial / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D003598:Cytoskeletal Proteins; C071525:FtsZ protein, Bacteria