MMS-INDUCED MUTAGENESIS AND DNA-REPAIR IN ESCHERICHIA-COLI DNAQ49 - CONTRIBUTION OF UMUD' TO DNA-REPAIR

dnaQ-encoded epsilon subunit of DNA polymerase III, possesses 3',5' ex onuclease (proofreading) activity, and is a fidelity factor of polymer ase III holoenzyme. It is assumed that during SOS-induced mutagenesis, UmuD', UmuC and RecA may suppress DnaQ proofreading activity, and all ow for translesional DNA synthesis at the cost of fidelity of replicat ion. In this report SOS-dependent, MMS-induced mutagenesis and DNA rep air were tested in E, coli dnaQ49 strains. Bacteria were transformed w ith various pDNAs harboring compilation of the umuD(D')C genes, and th e influence of plasmids on mutagenesis (argE3 --> Arg(+)) and DNA repa ir was tested. DNA damage and repair were tested in plasmid DNA grown in MMS-treated bacteria and isolated either immediately after MMS trea tment, 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 t he 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 main tenance of DNA integrity. The kinetics of these processes (perhaps due to introducing too many of the lesions) seems to be different in E. c oli dnaQ(+) and dnaQ cells, and probably this is a reason that (iii) M MS-induced mutations in dnaQ49 strains are not subject to MFD.