The effect of methylation on DNA replication in Salmonella enterica serovar typhimurium.

The DNA adenine methylase of Salmonella typhimurium methylates adenine at GATC sequences. Strains deficient in this methylase are not well transformed by methylated plasmids, but unmethylated plasmids transform them at high frequencies. Hemimethylated daughter molecules accumulate after the transformation of dam(-) strains with fully methylated plasmids, suggesting that hemimethylation prevents DNA replication.