MUTAGENIC REPAIR IN ESCHERICHIA-COLI - PRODUCTS OF THE RECA GENE AND OF THE UMUD AND UMUC GENES ACT AT DIFFERENT STEPS IN UV-INDUCED MUTAGENESIS
MUTAGENIC REPAIR IN ESCHERICHIA-COLI - PRODUCTS OF THE RECA GENE AND OF THE UMUD AND UMUC GENES ACT AT DIFFERENT STEPS IN UV-INDUCED MUTAGENESIS
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DOI：
10.1073/pnas.82.12.4193
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发表时间：
1985-01-01
影响因子：
11.1
通讯作者：
WOODGATE, R
中科院分区：
文献类型：
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作者：
BRIDGES, BA;WOODGATE, R
当携带umuc或umuD等位基因的切除缺陷的大肠杆菌在紫外线照射几小时后暴露在可见光下时，在这些通常不能紫外线突变的细菌中诱导了碱基对替换突变。有人认为，延迟的嘧啶二聚体的光逆转消除了DNA复制的障碍，并允许错误结合的碱基的存活和表达。提出了一种紫外线诱变模型，该模型包括两个步骤：与光产物相反的误掺入，它可以直接由RecA蛋白介导；绕过，后者只需要umuD+和UMUC+等位基因。基础水平的基因产物对于至少一些误掺入事件是足够的，尽管诱导水平的umuD和UMUC基因产物对于旁路步骤是必要的。在延迟光逆转后，含有recA441等位基因的UMUC细菌显示出更高的突变体产量，而含有recA430等位基因的UMUC细菌的产量降低。LexA51等位基因(导致RecA蛋白生产的结构性去抑制)没有显著改变突变株的产量，但导致它们在recA441 UMUC菌株中出现得更早。这些结果强调，RecA蛋白的性质而不是其浓度是决定误掺入水平的最重要因素。在43度下用recA441 UMUC细菌进行实验。C和30度。C提示，误掺入效应不太可能归因于DNA结合蛋白的裂解，如抑制子或聚合酶复合体的一个组成部分。在recA控制下，似乎在不需要诱导合成任何其他蛋白质的情况下发生了误掺入。
When excision-deficient E. coli carrying umuC or umuD alleles were exposed to visible light several hours after UV irradiation, base-pair-substitution mutations were induced in these normally non-UV-mutable bacteria. It is argued that delayed photoreversal of pyrimidine dimers removes blocks to DNA replication and allows the survival and expression of misincorporated bases. A model for UV mutagenesis is proposed with 2 steps: misincorporation opposite a photoproduct, which can be mediated directly by RecA protein; and bypass, only the latter process requiring umuD+ and umuC+ alleles. Basal levels of gene products are sufficient for at least some misincorporation events, although induced levels of umuD and umuC gene products are necessary for the bypass step. umuC bacteria containing the recA441 allele showed a greater yield of mutants, and those containing recA430 a reduced yield, following delayed photoreversal. The lexA51 allele (which results in constitutive derepression of RecA protein production) did not significantly alter the yield of mutants but caused them to appear marginally sooner in a recA441 umuC strain. These results emphasize that the nature of the RecA protein and not its concentration is paramount in determining the level of misincorporation. Experiments with recA441 umuC bacteria at 43.degree. C and 30.degree. C suggest that the misincorporation effect is unlikely to be attributable to cleavage of a DNA binding protein such as a repressor or a component of the polymerase complex. Misincorporation seems to occur without the need for induced synthesis of any other protein under recA control.