FEATURES

FAMILY

type-I restriction system S methylase family

DESCRIPTION

Also known as T1S1_ECOLX, hsdS, hss. The M and S subunits together form a methyltransferase (MTase) that methylates two adenine residues in complementary strands of a bipartite DNA recognition sequence. In the presence of the R subunit the complex can also act as an endonuclease, binding to the same target sequence but cutting the DNA some distance from this site. Whether the DNA is cut or modified depends on the methylation state of the target sequence. When the target site is unmodified, the DNA is cut. When the target site is hemimethylated, the complex acts as a maintenance MTase modifying the DNA so that both strands become methylated. Subunit S dictates DNA sequences specificity. The EcoR124/3i enzyme recognizes 5'-GAAN(6)RTCG-3'. The type I restriction/modification system is composed of three polypeptides R, M and S.

EXTERNAL LINKS

hsdS

Type-1 restriction enzyme EcoR124II specificity protein

hsdS

Molecular Synopsis