The DNA methylation is a post-replicative event that provides secondary information to that formed by DNA. Addition of this information involves DAM methyltransferase, which methylates DNA on specific sites (5'-GATC-3'). This modification of DNA may play a role in regulating various processes in eukaryote or prokaryote cells. It was well understood that deoxyadenosine methyltransferase (DAM) methylates the adenine of the GATC sequence. Following DNA replication, however, DNA is transiently hemimethylated, and the new strand is then methylated by DAM. In Escherichia coli, removing the dam gene produces several phenotypes indicating multiple functions of methylation: (i) modulation of gene expression, (ii) DNA repair, (iii) initiation of replication, and (iv) stabilising the chromosome.