EFFICIENCY OF MUCAB AND ESCHERICHIA-COLI UMUDC PROTEINS IN QUINOLONE AND UV MUTAGENESIS IN SALMONELLA-TYPHIMURIUM - EFFECT OF MUCA AND UMUDPROCESSING

The role of MucAB and Escherichia coli UmuDC proteins in mutagenesis b y 4-quinolone (4-Q) compared to that in UV mutagenesis has been studie d in hisG428 Salmonella typhimurium strains. A low-copy plasmid carryi ng mucAB genes, but not umuDC, promotes reversion of the hisG428 mutat ion by the 4-Q ciprofloxacin. In contrast, a umuDC plasmid mediates th e reversion of hisG428 by UV, although less efficiently than a mucAB o ne. In addition, a unique copy of mucAB genes is enough to promote UV mutagenesis, whereas, several copies of them are required to detect ci profloxacin mutagenesis. Therefore, the mutagenic repair of quinolone damage by MucAB proteins is not a very efficient process. The presence of an umuD'C plasmid but not a mucA'B one, slightly increases the rev ersion of the hisG428 mutation by ciprofloxacin and this finding is fu rther discussed. In contrast, MucA'B are still more active than UmuD'C proteins in UV mutagenesis. These results suggest that the enhanced p rocessing of MucA compared to UmuD would not explain all functional di fferences between MucAB and UmuDC proteins in the error-prone DNA repa ir.