New phenotypes associated with mucAB: alteration of a MucA sequence homologous to the XXXX cleavage site.

@entity6899 @entity4022 @entity367 @entity47397 @entity526
Most mutagenesis by UV and many chemicals in @entity526 requires the products of the umuDC operon or an analogous plasmid-derived operon mucAB. Activated RecA protein is also required for, or enhances, this process. MucA and UmuD proteins share homology with the @entity6899 protein, suggesting that they might interact with the RecA protein as @entity6899 does. We used oligonucleotide-directed mutagenesis to alter a site in MucA homologous to the Ala- @entity4022 cleavage site of @entity6899 . The mutation, termed mucA101( @entity367 26), results in a change of Gly26 of MucA to @entity367 26. A @entity6899 ( @entity47397 ) recA441 umuC122::Tn5 strain carrying a mucA101( @entity367 26)B+ plasmid did not exhibit the greatly increased frequency of spontaneous mutagenesis in response to RecA activation that a strain carrying a mucA+B+ plasmid did but retained a basal recA-dependent ability to confer increased spontaneous mutagenesis that was independent of the state of RecA activation. These results are consistent with a model in which RecA plays two distinct roles in mutagenesis apart from its role in the cleavage of @entity6899 . A pBR322-derived plasmid carrying mucA+B+, but not one carrying mucA101( @entity367 26)B+, inhibited the UV induction of SOS genes, suggesting that MucA+ and MucA( @entity367 26) proteins may have different abilities to compete with @entity6899 for activated RecA protein. The spectrum of UV-induced mutagenesis was also altered in strains carrying the mucA101( @entity367 26) mutation. These results are consistent with the hypothesis that activated RecA protein interacts with wild-type MucA protein, possibly promoting proteolytic cleavage, and that this interaction is responsible for facilitating certain mutagenic processes.
