Department of Microbiology, Immunology, and Molecular Genetics and the Molecular Biology Institute, University of California, and the David Geffen School of Medicine, Los Angeles, California, USA.
J Bacteriol. 2012 Oct;194(20):5613-20. doi: 10.1128/JB.00962-12. Epub 2012 Aug 17.
Polynucleotide phosphorylase (PNP) plays a central role in RNA degradation, generating a pool of ribonucleoside diphosphates (rNDPs) that can be converted to deoxyribonucleoside diphosphates (dNDPs) by ribonucleotide reductase. We report here that spontaneous mutations resulting from replication errors, which are normally repaired by the mismatch repair (MMR) system, are sharply reduced in a PNP-deficient Escherichia coli strain. This is true for base substitution mutations that occur in the rpoB gene leading to Rif(r) and the gyrB gene leading to Nal(r) and for base substitution and frameshift mutations that occur in the lacZ gene. These results suggest that the increase in the rNDP pools generated by polynucleotide phosphorylase (PNP) degradation of RNA is responsible for the spontaneous mutations observed in an MMR-deficient background. The PNP-derived pool also appears responsible for the observed mutations in the mutT mutator background and those that occur after treatment with 5-bromodeoxyuridine, as these mutations are also drastically reduced in a PNP-deficient strain. However, mutation frequencies are not reduced in a mutY mutator background or after treatment with 2-aminopurine. These results highlight the central role in mutagenesis played by the rNDP pools (and the subsequent dNTP pools) derived from RNA degradation.
多核苷酸磷酸化酶（PNP）在 RNA 降解中起着核心作用，产生核糖核苷二磷酸（rNDPs）池，该池可通过核糖核苷酸还原酶转化为脱氧核糖核苷二磷酸（dNDPs）。我们在这里报告，由于复制错误而自发产生的突变，通常由错配修复（MMR）系统修复，在 PNP 缺陷型大肠杆菌菌株中急剧减少。这对于导致 Rif（r）的 rpoB 基因中的碱基替换突变和导致 Nal（r）的 gyrB 基因中的碱基替换和移码突变以及 lacZ 基因中的碱基替换和移码突变都是如此。这些结果表明，多核苷酸磷酸化酶（PNP）降解 RNA 产生的 rNDP 池的增加是 MMR 缺陷背景中观察到的自发突变的原因。PNP 衍生的池似乎也负责观察到的 mutT 突变体背景中的突变以及在用 5-溴脱氧尿苷处理后发生的突变，因为这些突变在 PNP 缺陷型菌株中也急剧减少。然而，突变频率在 mutY 突变体背景或在用 2-氨基嘌呤处理后不会降低。这些结果突出了源自 RNA 降解的 rNDP 池（和随后的 dNTP 池）在诱变中的核心作用。
