Practice question

Escherichia coli possesses two major methyltransferases for restriction-modification protection. Dam methylase, deoxyadenosine methylase, recognizes palindromic 5'-GATC-3' and transfers a methyl group to N6 of adenine on both strands, influencing replication timing, mismatch repair, and gene regulation. Dcm methylase modifies internal cytosine in 5'-CCWGG-3' sequences. Methylation of GATC renders DNA resistant to cleavage by MboI which cuts only unmethylated sites, while DpnI requires Dam-methylated adenine for cutting. Understanding Dam methylation is essential for plasmid preparation, cloning, transformation, and restriction analysis protocols in molecular biology.