Gawel Damian, Pham Phuong T, Fijalkowska Iwona J, Jonczyk Piotr, Schaaper Roel M
Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
J Bacteriol. 2008 Mar;190(5):1730-42. doi: 10.1128/JB.01463-07. Epub 2007 Dec 21.
The dnaX36(TS) mutant of Escherichia coli confers a distinct mutator phenotype characterized by enhancement of transversion base substitutions and certain (-1) frameshift mutations. Here, we have further investigated the possible mechanism(s) underlying this mutator effect, focusing in particular on the role of the various E. coli DNA polymerases. The dnaX gene encodes the tau subunit of DNA polymerase III (Pol III) holoenzyme, the enzyme responsible for replication of the bacterial chromosome. The dnaX36 defect resides in the C-terminal domain V of tau, essential for interaction of tau with the alpha (polymerase) subunit, suggesting that the mutator phenotype is caused by an impaired or altered alpha-tau interaction. We previously proposed that the mutator activity results from aberrant processing of terminal mismatches created by Pol III insertion errors. The present results, including lack of interaction of dnaX36 with mutM, mutY, and recA defects, support our assumption that dnaX36-mediated mutations originate as errors of replication rather than DNA damage-related events. Second, an important role is described for DNA Pol II and Pol IV in preventing and producing, respectively, the mutations. In the system used, a high fraction of the mutations is dependent on the action of Pol IV in a (dinB) gene dosage-dependent manner. However, an even larger but opposing role is deduced for Pol II, revealing Pol II to be a major editor of Pol III mediated replication errors. Overall, the results provide insight into the interplay of the various DNA polymerases, and of tau subunit, in securing a high fidelity of replication.
大肠杆菌的 dnaX36(TS) 突变体赋予一种独特的突变表型，其特征为颠换碱基替换和某些（-1）移码突变增强。在此，我们进一步研究了这种突变效应潜在的可能机制，尤其关注各种大肠杆菌 DNA 聚合酶的作用。dnaX 基因编码 DNA 聚合酶 III（Pol III）全酶的 tau 亚基，该酶负责细菌染色体的复制。dnaX36 缺陷位于 tau 的 C 末端结构域 V，这对 tau 与 α（聚合酶）亚基的相互作用至关重要，表明突变表型是由 α - tau 相互作用受损或改变所致。我们先前提出，突变活性源于 Pol III 插入错误产生的末端错配的异常处理。目前的结果，包括 dnaX36 与 mutM、mutY 和 recA 缺陷缺乏相互作用，支持了我们的假设，即 dnaX36 介导的突变起源于复制错误而非与 DNA 损伤相关的事件。其次，描述了 DNA Pol II 和 Pol IV 在分别预防和产生突变方面的重要作用。在所用系统中，很大一部分突变以（dinB）基因剂量依赖的方式依赖于 Pol IV 的作用。然而，推断出 Pol II 具有更大但相反的作用，这表明 Pol II 是 Pol III 介导的复制错误的主要校正因子。总体而言，这些结果深入了解了各种 DNA 聚合酶以及 tau 亚基在确保高保真复制中的相互作用。
