Reassessment of the in vivo functions of DNA polymerase I and RNase h in bacterial cell growth
Reassessment of the in vivo functions of DNA polymerase I and RNase h in bacterial cell growth
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DOI：
10.1128/jb.00653-07
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发表时间：
2007-12-01
影响因子：
3.2
通讯作者：
Yoshikawa, Hirofumi
中科院分区：
文献类型：
--
作者：
Fukushima, Sanae;Itaya, Mitsuhiro;Yoshikawa, Hirofumi
在冈崎片段的加工过程中去除RNA引物的主要因素是DNA聚合酶I（Pol I）。Pol I被认为去除RNA引物并同时填充产生的缺口。由rnh基因编码的RNase H是去除RNA引物的另一个因素，关于polA和rnh基因的必要性存在分歧。在先前的研究中，我们寻找枯草芽孢杆菌中旁系同源物的合成致死性，并检测到几种必需的双联体旁系同源物，包括polA ypcP对。YpcP仅由5 '-3'核酸外切酶结构域组成。在本研究中，我们首次证实大肠杆菌和B. subtilis可以完全删除。我们发现由polA或ypcP xni编码的5 '-3'核酸外切酶活性是B生长所需的。枯草芽孢杆菌和E.杆菌Pol Ⅰ的5 ′-3 ′核酸外切酶活性在细长聚球藻中也是不可缺少的。这些结果表明，5 '-3'核酸外切酶活性在这些生物体中是必需的。我们在建造一个B。缺乏所有RNA酶H基因的枯草杆菌菌株的RNA酶活性表明酶活性是低的，至少在野生型中是低的。增加5 '-3'核酸外切酶活性部分补偿了RNase H缺陷突变体的缺陷表型，表明两种酶系统的协同功能。我们在250个细菌基因组中寻找5 '-3'核酸外切酶结构域的分布，结果发现所有真细菌，而不是古细菌，都具有这个结构域。
A major factor in removing RNA primers during the processing of Okazaki fragments is DNA polymerase I (Pol I). Pol I is thought to remove the RNA primers and to fill the resulting gaps simultaneously. RNase H, encoded by rnh genes, is another factor in removing the RNA primers, and there is disagreement with respect to the essentiality of both the polA and rnh genes. In a previous study, we looked for the synthetic lethality of paralogs in Bacillus subtilis and detected several essential doublet paralogs, including the polA ypcP pair. YpcP consists of only the 5'-3' exonuclease domain. In the current study, we first confirmed that the polA genes of both Escherichia coli and B. subtilis could be completely deleted. We found that the 5'-3' exonuclease activity encoded by either polA or ypcP xni was required for the growth of B. subtilis and E. coli. Also, the 5'-3' exonuclease activity of Pol I was indispensable in the cyanobacterium Synechococcus elongatus. These results suggest that a 5'-3' exonuclease activity is essential in these organisms. Our success in constructing a B. subtilis strain that lacked all RNase H genes indicates that the enzymatic activity is dispensable, at least in the wild type. Increasing the 5'-3' exonuclease activity partially compensated for a defective phenotype of an RNase H-deficient mutant, suggesting cooperative functions for the two enzyme systems. Our search for the distribution of the 5'-3' exonuclease domain among 250 bacterial genomes resulted in the finding that all eubacteria, but not archaea, possess this domain.