Isolation and characterization of Dam+ revertants and suppressor mutations that modify secondary phenotypes of dam-3 strains of Escherichia coli K-12.

Bacteria mutant in the dam (DNA adenine methylation) gene and in either recA or recB or recC genes are inviable (Virm- phenotype). From crosses between dam-3 bacteria and recA1 or recB21 recC22 strains, Vrm+ recombinants were recovered. Among these recombinants, Dam+ revertants were present which did not show the phenotypes normally associated with dam-3 bacteria. Three classes of indirectly suppressed strains (dam-3 genotype) were also recovered which showed alterations in the secondary phenotypes normally associated with dam-3 bacteria. These strains contained a second unlinked mutation in either mutL or mutS or sin. In addition, mutation in either sbcA or sbcB supresses the Vrm- phenotype of dam-3 recB21 recC22 strains.