A strain of Escherichia coli K12 mutant at the dam†† Abbreviations used: dam, DNA adenine methylase; 6-MeA, N,66-methyladenine; 5-MeC, 5-methylcytosine; hsp, host specificity. site contains 0.8 mole % 6-methyl adenine as compared to 0.50 mole % in the wild type, and the residual DNA methylation is not due to the K12 modification methylase specified by the hsp genes. The dam-3 mutant is more sensitive to ultraviolet irradiation and to mitomycin C than the wild type and also shows a higher mutability. DNA isolated from the dam-3 mutant contains single-stranded breaks that are amplified in dam-3 polA12 and dam-3 lig-7 double mutants. A function of dam-specified 6-methyl adenine residues in DNA would, therefore, appear to be the protection of DNA from a nuclease(s) that causes the development of breaks. Combination of dam-3 with polA, recA, recB and recC is lethal. © 1974.
Marinus, M. G., & Morris, N. R. (1974). Biological function for 6-methyladenine residues in the DNA of Escherichia coli K12. Journal of Molecular Biology, 85(2), 309–322. https://doi.org/10.1016/0022-2836(74)90366-0