Sassanfar M, Roberts J
Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853.
J Bacteriol. 1991 Sep;173(18):5869-75. doi: 10.1128/jb.173.18.5869-5875.1991.
The recF143 mutant of Escherichia coli is deficient in certain functions that also require the RecA protein: cell survival after DNA damage, some pathways of genetic recombination, and induction of SOS genes and temperate bacteriophage through cleavage of the LexA and phage repressors. To characterize the role of RecF in SOS induction and RecA activation, we determined the effects of the recF143 mutation on the rate of RecA-promoted cleavage of LexA, the repressor of the SOS genes. We show that RecA activation following UV irradiation is delayed by recF143 and that RecF is specifically involved in the SOS induction pathway that requires DNA replication. At 32 degrees C, the recA441 mutation partially suppresses the defect of recF mutants in inducing the SOS system in response to UV irradiation (A. Thomas and R. G. Lloyd, J. Gen. Microbiol. 129:681-686, 1983; M. R. Volkert, L. J. Margossian, and A. J. Clark, J. Bacteriol. 160:702-705, 1984); we find that this suppression occurs at the earliest detectable phase of LexA cleavage and does not require protein synthesis. Our results support the idea that following UV irradiation, RecF enhances the activation of RecA into a form that promotes LexA cleavage (A. Thomas and R. G. Lloyd, J. Gen. Microbiol. 129:681-686, 1983; M. V. V. S. Madiraju, A. Templin, and A. J. Clark, Proc. Natl. Acad. Sci. USA 85:6592-6596, 1988). In contrast to the constitutive activation phenotype of the recA441 mutant, the recA441-mediated suppression of recF is not affected by adenine and nucleosides. We also find that wild-type RecA protein is somewhat activated by adenine in the absence of DNA damage.
大肠杆菌的recF143突变体在某些也需要RecA蛋白的功能方面存在缺陷：DNA损伤后的细胞存活、一些基因重组途径，以及通过LexA和噬菌体阻遏物的裂解来诱导SOS基因和温和噬菌体。为了表征RecF在SOS诱导和RecA激活中的作用，我们确定了recF143突变对RecA促进的SOS基因阻遏物LexA裂解速率的影响。我们表明，recF143会延迟紫外线照射后RecA的激活，并且RecF特别参与需要DNA复制的SOS诱导途径。在32℃时，recA441突变部分抑制了recF突变体在响应紫外线照射时诱导SOS系统的缺陷（A.托马斯和R.G.劳埃德，《普通微生物学杂志》129:681 - 686，1983；M.R.沃尔克特、L.J.马戈西安和A.J.克拉克，《细菌学杂志》160:702 - 705，1984）；我们发现这种抑制发生在LexA裂解最早可检测的阶段，并且不需要蛋白质合成。我们的结果支持这样一种观点，即紫外线照射后，RecF增强了RecA激活为促进LexA裂解的形式（A.托马斯和R.G.劳埃德，《普通微生物学杂志》129:681 - 686，1983；M.V.V.S.马迪拉朱、A.坦普林和A.J.克拉克，《美国国家科学院院刊》85:6592 - 6596，1988）。与recA441突变体的组成型激活表型相反，recA441介导的recF抑制不受腺嘌呤和核苷的影响。我们还发现，在没有DNA损伤的情况下，野生型RecA蛋白会被腺嘌呤部分激活。
