Kadoya Ryosuke, Hassan Anwarul K M, Kasahara Yasuhiro, Ogasawara Naotake, Moriya Shigeki
Graduate School of Biological Sciences, nara Institue of Science and Technology, Takayama, Ikoma, Nara, Japan.
Mol Microbiol. 2002 Jul;45(1):73-87. doi: 10.1046/j.1365-2958.2002.03016.x.
Current views of bacterial chromosome segregation vary in respect of the likely presence or absence of an active segregation mechanism involving a mitotic-like apparatus. Furthermore, little is known about cis-acting elements for chromosome segregation in bacteria. In this report, we show that two separate DNA regions, a 3' coding region of dnaA and the AT-rich sequence between dnaA and dnaN (the initial opening site of duplex DNA during replication), are necessary for efficient segregation of the chromosome in Bacillus subtilis. When a plasmid replicon was integrated into argG, far from oriC, on the chromosome and then the oriC function was disrupted, the oriC-deleted mutant formed anucleate cells at 5% possibly because of defects in chromosome segregation. However, when the two DNA sequences were added near oriN, frequency of anucleate cells decreased to 1%. In these cells, the origin (argG) regions were localized near cell poles, whereas they were randomly distributed in cells without the two DNA sequences. These results suggest that the two DNA sequences in and downstream of the dnaA gene participate in correct positioning of the replication origin region within the cell and that this function is associated with accurate chromosome segregation in B. subtilis.
目前对于细菌染色体分离的观点，在是否可能存在涉及类似有丝分裂装置的主动分离机制方面存在差异。此外，关于细菌中染色体分离的顺式作用元件知之甚少。在本报告中，我们表明两个独立的DNA区域，即dnaA的3'编码区以及dnaA和dnaN之间富含AT的序列（复制过程中双链DNA的初始开放位点），对于枯草芽孢杆菌中染色体的有效分离是必需的。当一个质粒复制子整合到染色体上远离oriC的argG处，然后oriC功能被破坏时，oriC缺失突变体可能由于染色体分离缺陷而在5%的情况下形成无核细胞。然而，当这两个DNA序列添加到oriN附近时，无核细胞的频率降至1%。在这些细胞中，起源（argG）区域位于细胞极附近，而在没有这两个DNA序列的细胞中它们是随机分布的。这些结果表明，dnaA基因内部及其下游的两个DNA序列参与了复制起始区域在细胞内的正确定位，并且该功能与枯草芽孢杆菌中准确的染色体分离相关。
