DNA replication of the two Vibrio cholerae chromosomes

霍乱弧菌是人类历史上最致命的病原体之一。它是霍乱的病原体，霍乱是一种以大量水样腹泻为特征的疾病。日益严重的大流行性霍乱问题是由耐抗生素菌株引起的。寻找新的特异性药物靶点需要对霍乱弧菌的生物学有深入的了解，近年来人们把重点放在了霍乱弧菌独特的基因组排列上。虽然大多数细菌在一条染色体上携带它们的遗传信息，但霍乱弧菌的基因组在两条染色体上分裂，就像几乎所有弧菌属成员的情况一样。霍乱弧菌染色体Chr1和Chr2的大小分别约为3和1 Mbps。两条染色体中的每一条的DNA复制都是从一个复制起点开始的，其中ori1的调控依赖于启动蛋白DNA，而ori2依赖于弧菌特异性蛋白RctB。有趣的是，Chr2复制是在大约三分之二的Chr1被复制后开始的，导致两个复制子的复制同步终止。最近发现，这种时间依赖于位于Chr1上的一种新的DNA序列，称为crtS （Chr2触发位点）。结果表明，DNA复制过程中crtS的加倍触发了ori2的起始。然而，我们对这一机制的了解是不完整的，因此我们的工作主要集中在crt网站上。一组遗传学和基因组学实验计划研究基于crt的Chr2复制触发。此外，我们假设霍乱弧菌复制起源调控还涉及其他未知因素。我们打算使用高通量遗传筛选来发现这些预测的未知因素。确定一种新的调节剂将开辟一条令人兴奋的研究重点新途径。

Vibrio cholerae is one of the deadliest pathogens in the history of humankind. It is the causative agent of cholera, a disease characterized by a profuse and watery diarrhea. A growing problem of pandemic cholera is caused by antibiotic resistant strains. The search for novel and specific drug targets requires a deep understanding of the V. cholerae biology and one focus was laid on the peculiar genome arrangement in recent years. While most bacteria carry their genetic information on a single chromosome, the genome of V. cholerae is split on two chromosomes as it is the case for almost all members of the genus Vibrio. The size of the Chr1 and Chr2 of V. cholerae chromosomes is about 3 and 1 Mbps, respectively. DNA replication of each of the two chromosomes is initiated at a single replication origin with ori1 regulation being dependent on the initiator protein DnaA and ori2 on the Vibrio-specific protein RctB. Interestingly, Chr2 replication is initiated after about two thirds of Chr1 are replicated leading to synchronous termination of replication of the two replicons. This timing was recently found to be dependent on a novel DNA sequence designated crtS (Chr2 triggering site) located on Chr1. It was shown that doubling of the crtS by the process of DNA replication triggers the initiation at ori2. However, our knowledge about this mechanism is only incomplete and consequently we mainly focus our work on the crtS site. A set of genetic and genomics experiments is planned to study the crtS-based triggering of Chr2 replication. In addition, we hypothesize that additional unknown factors are involved in V. cholerae replication origin regulation. We intent to find such predicted as-of-yet unknown factors using a high-throughput genetic screen. Identification of a new regulator would open up an exciting new avenue of research focus.