Biological role of DNA methylation: sequence-specific single-strand breaks associated with hypomethylation of GATC sites in Escherichia coli DNA.

The effect of methylation of GATC sites in Escherichia coli DNA on the formation of single-strand breaks was studied with dam+, dam mutant, and Dam-overproducer strains. Single-strand breaks have been observed in dam mutant cells predominantly at TpT and, to a lesser extent, at CpC. In dam mutant cells harboring pTP166 (a plasmid containing the dam gene), no such nicks were observed.