Grzesiuk E, Janion C
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland.
Mutat Res. 1996 Feb 15;362(2):147-54. doi: 10.1016/0921-8777(95)00035-6.
dnaQ-encoded epsilon subunit of DNA polymerase III, possesses 3',5' exonuclease (proofreading) activity, and is a fidelity factor of polymerase III holoenzyme. It is assumed that during SOS-induced mutagenesis, UmuD', UmuC, and RecA may suppress DnaQ proofreading activity, and allow for translesional DNA synthesis at the cost of fidelity of replication. In this report SOS-dependent, MMS-induced mutagenesis and DNA repair were tested in E. coli dnaQ49 strains. Bacteria were transformed with various pDNAs harboring compilation of the umuD(D')C genes, and the influence of plasmids on mutagenesis (argE3-->Arg+) and DNA repair was tested. DNA damage and repair were tested in plasmid DNA grown in MMS-treated bacteria and isolated either immediately after MMS treatment, or after starving the cells (MFD conditions) for 30 and 60 min, then nicking activity of Fpg protein on plasmid DNAs was analyzed. It has been found that (i) repair of MMS-induced lesions depends on umuD'C, umuD' (and to much less degree, on umuDC) genes encoded in pDNA; (ii) MMS-induced mutations, in contrast to DNA repair, are highest in the cells transformed with pDNA harboring umuDC, and lowest or zero in cells with plasmids harboring umuD'C. It is postulated that UmuD'C or UmuD' proteins play a role in the repair of damaged DNA and/or in maintenance of DNA integrity. The kinetics of these processes (perhaps due to introducing too many of the lesions) seems to be different in E. coli dnaQ+ and dnaQ cells, and probably this is a reason that (iii) MMS-induced mutations in dnaQ49 strains are not subject to MFD.
DNA聚合酶III的dnaQ编码的ε亚基具有3',5'核酸外切酶（校对）活性，是聚合酶III全酶的保真因子。据推测，在SOS诱导的诱变过程中，UmuD'、UmuC和RecA可能会抑制DnaQ的校对活性，并以复制保真度为代价允许跨损伤DNA合成。在本报告中，对大肠杆菌dnaQ49菌株中SOS依赖性的、甲基磺酸甲酯（MMS）诱导的诱变和DNA修复进行了测试。用携带umuD(D')C基因组合的各种pDNA转化细菌，并测试质粒对诱变（argE3→Arg+）和DNA修复的影响。在MMS处理的细菌中生长的质粒DNA中测试DNA损伤和修复，这些质粒DNA在MMS处理后立即分离，或在使细胞饥饿（MFD条件）30分钟和60分钟后分离，然后分析Fpg蛋白对质粒DNA的切口活性。已发现：（i）MMS诱导损伤的修复取决于pDNA中编码的umuD'C、umuD'（以及程度小得多的umuDC）基因；（ii）与DNA修复相反，MMS诱导的突变在用携带umuDC的pDNA转化的细胞中最高，而在用携带umuD'C的质粒的细胞中最低或为零。据推测，UmuD'C或UmuD'蛋白在受损DNA的修复和/或DNA完整性的维持中起作用。这些过程的动力学（可能是由于引入了太多损伤）在大肠杆菌dnaQ+和dnaQ细胞中似乎不同，这可能是（iii）dnaQ49菌株中MMS诱导的突变不受MFD影响的原因。
