DNA adenine methylation is required to replicate both Vibrio cholerae chromosomes once per cell cycle.
DNA adenine methylation is required to replicate both Vibrio cholerae chromosomes once per cell cycle.
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DOI：
10.1371/journal.pgen.1000939
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发表时间：
2010-05-06
期刊：
影响因子：
4.5
通讯作者：
Chattoraj DK
中科院分区：
文献类型：
--
作者：
Demarre G;Chattoraj DK
DNA腺嘌呤甲基化被广泛用于控制许多DNA交易，包括复制。在大肠杆菌中，甲基化用于沉默新合成的（半甲基化的）姊妹源。SeqA是一种与半甲基化DNA结合的蛋白质，它介导沉默，这对于将复制限制在每个细胞周期一次是必要的。然而，甲基化本身并不是开始复制所必需的，但当两条霍乱弧菌染色体的起源（oriI和oriII）在大肠杆菌中用于驱动质粒复制时，甲基化就出现了。在这里，我们表明，就像在大肠杆菌的情况下一样，当oriI驱动染色体复制时，甲基化不是必需的，并且需要以依赖seqa的方式进行每细胞周期一次的复制。我们发现，oriII还需要SeqA来完成每细胞周期一次的复制，此外，为了有效地结合引发剂，还需要完全甲基化。对引发剂结合的要求可能足以使甲基化成为霍乱弧菌的基本功能。oriII的结构表明它起源于质粒，但与质粒不同的是，oriII利用甲基化进行每细胞周期一次的复制，这是染色体复制的标准，而不是质粒复制的标准。细菌通常只有一条染色体，但也有染色体外复制子，称为质粒。虽然通常是不可缺少的，但质粒可以赋予细胞在压力环境中的适应性优势。细菌也可以有多条染色体，每条染色体都携带必要的基因，就像真核生物一样。在所有生物体中，染色体在细胞分裂之前都会复制一次，这样子细胞就可以得到相同的遗传嫁妆，但细菌质粒通常不是这样。霍乱的病原体霍乱弧菌有一条典型的细菌染色体，就像被充分研究过的大肠杆菌的染色体一样，它还有一条带有许多特征的第二条染色体，表明它起源于一个质粒。在这里，我们表明，尽管两条染色体的性质不同，但它们每个细胞周期都复制一次，并且它们都需要DNA腺嘌呤甲基化来实现这一目的。我们的研究表明，在多染色体细菌中，每细胞周期复制一次是染色体的必要特征，并提供了甲基化如何赋予染色体外复制子像染色体一样复制能力的范例。
DNA adenine methylation is widely used to control many DNA transactions, including replication. In Escherichia coli, methylation serves to silence newly synthesized (hemimethylated) sister origins. SeqA, a protein that binds to hemimethylated DNA, mediates the silencing, and this is necessary to restrict replication to once per cell cycle. The methylation, however, is not essential for replication initiation per se but appeared so when the origins (oriI and oriII) of the two Vibrio cholerae chromosomes were used to drive plasmid replication in E. coli. Here we show that, as in the case of E. coli, methylation is not essential for oriI when it drives chromosomal replication and is needed for once-per-cell-cycle replication in a SeqA-dependent fashion. We found that oriII also needs SeqA for once-per-cell-cycle replication and, additionally, full methylation for efficient initiator binding. The requirement for initiator binding might suffice to make methylation an essential function in V. cholerae. The structure of oriII suggests that it originated from a plasmid, but unlike plasmids, oriII makes use of methylation for once-per-cell-cycle replication, the norm for chromosomal but not plasmid replication. Bacteria usually have one chromosome but can have extrachromosomal replicons, called plasmids. Although normally dispensable, plasmids can confer adaptive advantage to cells in stressful environments. Bacteria can also have multiple chromosomes, each carrying essential genes, as in eukaryotes. In all organisms, chromosomes duplicate once before the cells divide so that the daughter cells can receive equal genetic dowry, but this is not usually the case with bacterial plasmids. Vibrio cholerae, the causative agent for the disease cholera, has a typical bacterial chromosome like the chromosome of the well-studied bacterium Escherichia coli and has a second chromosome with many signatures indicating its origin from a plasmid. Here we show that, in spite of the distinct nature of the two chromosomes, they both duplicate once per cell cycle, and they both require DNA adenine methylation for this purpose. Our study suggests that once-per-cell-cycle replication is a necessary feature of a chromosome in multichromosome bacteria, and provides a paradigm of how methylation could endow extrachromosomal replicons with the capacity to duplicate like chromosomes.
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