Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Quartier UNIL/Sorge, Lausanne, CH 1015, Switzerland.
Plasmid. 2012 Mar;67(2):76-87. doi: 10.1016/j.plasmid.2011.12.007. Epub 2011 Dec 29.
The alpha-proteobacterium Caulobacter crescentus is characterized by its asymmetric cell division, which gives rise to a replicating stalked cell and a non-replicating swarmer cell. Thus, the initiation of chromosomal replication is tightly regulated, temporally and spatially, to ensure that it is coordinated with cell differentiation and cell cycle progression. Waves of DnaA and CtrA activities control when and where the initiation of DNA replication will take place in C. crescentus cells. The conserved DnaA protein initiates chromosomal replication by directly binding to sites within the chromosomal origin (Cori), ensuring that DNA replication starts once and only once per cell cycle. The CtrA response regulator represses the initiation of DNA replication in swarmer cells and in the swarmer compartment of pre-divisional cells, probably by competing with DnaA for binding to Cori. CtrA and DnaA are controlled by multiple redundant regulatory pathways that include DNA methylation-dependent transcriptional regulation, temporally regulated proteolysis and the targeting of regulators to specific locations within the cell. Besides being critical regulators of chromosomal replication, CtrA and DnaA are also master transcriptional regulators that control the expression of many genes, thus connecting DNA replication with other events of the C. crescentus cell cycle.
α-变形菌新月柄杆菌的特点是不对称细胞分裂，这导致了一个复制的柄细胞和一个非复制的游动细胞。因此，染色体复制的起始受到严格的时空调控，以确保其与细胞分化和细胞周期进程相协调。DnaA 和 CtrA 活性波控制着 C. crescentus 细胞中 DNA 复制的起始时间和位置。保守的 DnaA 蛋白通过直接结合染色体起始点（oriC）内的位点来启动染色体复制，从而确保每个细胞周期只起始一次 DNA 复制。CtrA 反应调节蛋白抑制游动细胞和预分裂细胞游动区的 DNA 复制起始，可能通过与 DnaA 竞争结合 oriC 来实现。CtrA 和 DnaA 受多种冗余调节途径控制，包括 DNA 甲基化依赖的转录调控、时间调节的蛋白水解和调节因子靶向细胞内特定位置。除了作为染色体复制的关键调节因子外，CtrA 和 DnaA 也是控制许多基因表达的主要转录调节因子，从而将 DNA 复制与新月柄杆菌细胞周期的其他事件联系起来。
