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首页> 外文期刊>Journal of bacteriology >Intrinsic Polymerase Activities of UmuD′2C and MucA′2B Are Responsible for Their Different Mutagenic Properties during Bypass of a T-T cis-synCyclobutane Dimer
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Intrinsic Polymerase Activities of UmuD′2C and MucA′2B Are Responsible for Their Different Mutagenic Properties during Bypass of a T-T cis-synCyclobutane Dimer

机译：UmuD'2C和MucA'2B的内在聚合酶活性对绕过T-T顺式-顺式环丁烷二聚物的不同诱变特性负责

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In wild-type Escherichia coli, translesion replication is largely dependent upon the UmuD′2C complex (DNA polymerase V [polV]) or its plasmid-encoded homologs, such as MucA′2B. Interestingly, both the efficiency of translesion replication of a T-T cis-syn dimer and the spectra of mutations observed are different in Umu- and Muc-expressing strains. We have investigated whether the polIII core is responsible for these differences by measuring the frequency of dimer bypass, the error rate of bypass, and the resulting mutation spectrum in mutants carrying a deletion of dnaQ (? subunit) or holE (θ subunit) or carrying the dnaQ allele mutD5, which is deficient in proofreading but is competent in the structural function of ?, or the dnaE antimutator allelespq-2. The chromosomal copy of the umuDC operon was deleted in each strain, and the UmuDC, UmuD′C, MucAB, or MucA′B proteins were expressed from a low-copy-number plasmid. With only few exceptions, we found that the characteristically different mutation spectra resulting from Umu- and Muc-mediated bypass are maintained in all of the strains investigated, indicating that differences in the activity or structure of the polIII core are not responsible for the observed phenotype. We also demonstrate that the MucA′2B complex is more efficient in promoting translesion replication than the UmuD′2C proteins and show that, contrary to expectation, the T-T dimer is bypassed more accurately by MucA′2B than by UmuD′2C. These results are consistent with the view that in a wild-type cell, the polV-like enzymes are responsible for the spectra of mutations generated during translesion replication and that polIII may simply be required to fix the misincorporations as mutations by completing chromosomal replication. Our observations also show that the mutagenic properties of a lesion can depend strongly on the particular enzyme employed in bypass.
机译：在野生型大肠杆菌中，病灶的复制很大程度上取决于UmuD' 2 C复合物（DNA聚合酶V [polV]）或其质粒编码的同源物，例如MucA' 2 B。有趣的是，在表达Umu和Muc的菌株中，T-T 顺式-syn 二聚体的病灶复制效率和观察到的突变谱均不同。我们通过测量二聚体旁路的频率，旁路的错误率以及带有 dnaQ （？亚基）缺失的突变体中的突变谱，研究了polIII核心是否负责这些差异。 holE （θ亚基）或携带 dnaQ 等位基因 mutD5 ，虽然校对能力差，但能胜任α或 dnaE 抗突变等位基因 spq-2 。在每个菌株中删除了 umuDC 操纵子的染色体拷贝，并从低拷贝数质粒表达了UmuDC，UmuD'C，MucAB或MucA'B蛋白。除少数例外，我们发现在所有研究的菌株中均维持了由Umu和Muc介导的旁路产生的特征不同的突变谱，这表明polIII核心的活性或结构差异与观察到的表型无关。 。我们还证明了MucA' 2 B复合物比UmuD' 2 C蛋白在促进跨膜复制方面更有效，并且与预期相反，TT二聚体是MucA' 2 B比UmuD' 2 C更准确地绕过。这些结果与以下观点相一致：在野生型细胞中，polV样酶负责在病灶复制过程中产生的突变谱，并且可能只需要polIII即可通过完成染色体复制来将错误掺入固定为突变。我们的观察结果还表明，病变的诱变特性可能在很大程度上取决于旁路使用的特定酶。

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