CHARACTERIZATION OF DNA ADENINE METHYLATION MUTANTS OF ESCHERICHIA-COLI-K12

The phenotypic traits of 7 independently isolated dam mutants of Escherichia coli have been examined. The mutant strains differ from the wildtype in the following respects: (1) decreased DNA adenine methylase activity in vivo and in vitro; (2) a 14-85-fold increase in spontaneous mutability; (3) decreased survival after ultraviolet irradiation; (4) a 10-21-fold increase in spontaneous induction of λ phage from lysogens; (5) a 3-17-fold increase in the level of recombination; and (6) inviability of double mutants containing dam- and 3itrecB- or recC-. Unmethylated fd phage chromosomes are able to replicate normally in dam- mutants. A mutant strain in which the dcm gene is deleted is viable, showing that the dcm gene product is dispensible for growth. © 1979.