Prokaryotes predominantly contain N-6 adenine (A)-specific DNA methylases, which contain DNA methylase adenine-specific (IPR003356) domains. These enzymes are responsible for methylating specific DNA sequences in order to prevent the host from degrading its own genome through restriction endonucleases. These methylases exhibit the same sequence specificity as their respective restriction endonucleases. The M and S subunits form a methyltransferase, methylating both adenine residues in the complementary strands of the bipartite DNA recognition sequences. The complex can also function as an endonuclease in the presence of the R subunit, binding to the same target sequence but cleaving the DNA at a distance from the site. The methylation status of the target sequence dictates the cleavage or modification of the DNA. The DNA is cleaved when the target site remains unaltered. When the target site becomes hemimethylated, the complex acts as a maintenance methyltransferase, modifying the DNA to methylate both strands.