Department of Life Sciences and Institute of Genome Sciences, Institute of Biotechnology in Medicine, National Yang-Ming University, Shih-Pai, Taipei 11221, Taiwan.
Nucleic Acids Res. 2012 Feb;40(3):1118-30. doi: 10.1093/nar/gkr856. Epub 2011 Oct 17.
Linear chromosomes and linear plasmids of Streptomyces are capped by terminal proteins that are covalently bound to the 5'-ends of DNA. Replication is initiated from an internal origin, which leaves single-stranded gaps at the 3'-ends. These gaps are patched by terminal protein-primed DNA synthesis. Streptomyces contain five DNA polymerases: one DNA polymerase I (Pol I), two DNA polymerases III (Pol III) and two DNA polymerases IV (Pol IV). Of these, one Pol III, DnaE1, is essential for replication, and Pol I is not required for end patching. In this study, we found the two Pol IVs (DinB1 and DinB2) to be involved in end patching. dinB1 and dinB2 could not be co-deleted from wild-type strains containing a linear chromosome, but could be co-deleted from mutant strains containing a circular chromosome. The resulting ΔdinB1 ΔdinB2 mutants supported replication of circular but not linear plasmids, and exhibited increased ultraviolet sensitivity and ultraviolet-induced mutagenesis. In contrast, the second Pol III, DnaE2, was not required for replication, end patching, or ultraviolet resistance and mutagenesis. All five polymerase genes are relatively syntenous in the Streptomyces chromosomes, including a 4-bp overlap between dnaE2 and dinB2. Phylogenetic analysis showed that the dinB1-dinB2 duplication occurred in a common actinobacterial ancestor.
线性染色体和线性质粒的链霉菌是由末端蛋白共价结合在 DNA 的 5'端帽。复制是从内部起源开始的，这会在 3'端留下单链缺口。这些缺口通过末端蛋白引发的 DNA 合成进行修复。链霉菌含有五种 DNA 聚合酶：一种 DNA 聚合酶 I（Pol I）、两种 DNA 聚合酶 III（Pol III）和两种 DNA 聚合酶 IV（Pol IV）。其中，一种 Pol III（DnaE1）是复制所必需的，而 Pol I 不需要参与末端修复。在这项研究中，我们发现两种 Pol IV（DinB1 和 DinB2）参与了末端修复。在含有线性染色体的野生型菌株中，dinB1 和 dinB2 不能同时缺失，但在含有圆形染色体的突变型菌株中可以同时缺失。产生的ΔdinB1ΔdinB2 突变体支持圆形质粒的复制，但不支持线性质粒的复制，并且表现出增强的紫外线敏感性和紫外线诱导的突变率。相比之下，第二种 Pol III（DnaE2）对复制、末端修复和紫外线抗性及突变率都不是必需的。在链霉菌染色体中，所有五个聚合酶基因相对同源，包括 dnaE2 和 dinB2 之间的 4 个碱基重叠。系统发育分析表明，dinB1-dinB2 重复发生在一个共同的放线菌祖先中。
