Characterization of Escherichia coli Dam mutations

PANZETTA, MARIA EMILIA; MARTINA, M. ANDREA; BARRA, J. LUIS

Rosario

Congreso; L Reunión anual SAIB; 2014

SAIB

Escherichia coli strains deficient in DNA adenine methyltransferase (Dam) are mutators, and this deficiency also results in transcriptional defects of several genes. We have isolated some E. coli mutants that have partially affected Dam functions. These strains display some phenotypes similar to a Dam deficient strain but have a normal level of DNA methylation in stationary phase. Complementation assays showed that expression of the wild type dam gene reverts the phenotype of these strains. DNA sequencing of the endogenous dam gene revealed the presence of several mutations in the promoters and the coding sequence. Chimeric constructs between the wild type and a mutant dam gene allowed us to identify at least two different mutations able to generate this phenotype. E. coli Dam mutants carrying the chimeric constructs containing at least one of these mutations behave similar to the Dam deficient strain in the presence of a mutagen in liquid media. However, these strains behave like the wild type strain when the presence of the same mutagen was analyzed on solid culture media. In addition, after exposure to UV light, while dam strains are more sensitive to this agent than the wild type strain, those carrying the chimeric constructs were even more resistant. These phenotypes suggest that these kinds of Dam mutations could result advantageous for E. coli adaptation and/or evolution.