Kono Nobuaki, Arakawa Kazuharu, Sato Mitsuru, Yoshikawa Hirofumi, Tomita Masaru, Itaya Mitsuhiro
Institute for Advanced Biosciences, Keio University, Yamagata 997-0017, Japan.
Institute for Advanced Biosciences, Keio University, Yamagata 997-0017, Japan.
J Mol Biol. 2014 Aug 12;426(16):2918-27. doi: 10.1016/j.jmb.2014.06.005. Epub 2014 Jun 16.
The oriC DNA replication origin in bacterial chromosomes, the location of which appears to be physically identified, is genetically regulated by relevant molecular machinery. In contrast, the location of the terminus remains obscure for many bacterial replicons, except for terC, the proposed and well-studied chromosome termination site in certain bacteria. The terC locus, which is composed of specific sequences for its binding protein, is located at a site opposite from oriC, exhibiting a symmetric structure around the oriC-terC axis. Here, we investigated Bacillus subtilis 168 strains whose axes were hindered and found that the native terC function was robust. However, eradication of terminus region specific binding protein resulted in the natural terC sites not being used for termination; instead, new termini were selected at a location exactly opposite to oriC. We concluded that replication generally terminates at the loci where the two approaching replisomes meet. This site was automatically selected, and two replisomes moving at the same rate supported symmetrical chromosome structures relative to oriC. The rule, which was even validated by artificial chromosomes irrespective of oriC, should be general for replicons administered by two replisomes.
细菌染色体中的oriC DNA复制起点，其位置似乎已在物理上得到确定，受到相关分子机制的遗传调控。相比之下，除了某些细菌中已提出并深入研究的染色体终止位点terC外，许多细菌复制子的终点位置仍不清楚。terC位点由其结合蛋白的特定序列组成，位于与oriC相对的位置，围绕oriC - terC轴呈现对称结构。在此，我们研究了轴受到阻碍的枯草芽孢杆菌168菌株，发现天然的terC功能很强。然而，去除终点区域特异性结合蛋白导致天然的terC位点未被用于终止；相反，新的终点在与oriC正好相对的位置被选择。我们得出结论，复制通常在两个接近的复制体相遇的位点终止。这个位点是自动选择的，以相同速率移动的两个复制体支持相对于oriC的对称染色体结构。这条规则甚至通过人工染色体得到验证，与oriC无关，对于由两个复制体管理的复制子应该是普遍适用的。
