[Isolation and properties of DNA-cytosine-methyltransferase EcoRII and E. coli K12]

The methods of isolation and partial purification of two DNA-cytosine-methylases (DC-methylases) EcoRII and E. coli K12 are described. After chromatography on phosphocellulose the enzymes were purified 100-fold, the yield being 30%. Further purification of the enzymes was performed by sedimentation in a sucrose concentration gradient. Both enzymes have native molecular weights of 50,000; DC-methylase from E. coli K12 may simultaneously occur in the forms with molecular weights of 70,000, 90,000 and 110,000. Both DC-methylases modify identical nucleotide sequences of DNA, have equal numbers (90) of methylation sites in phage lambda DNA and provide in vitro a complete protection of phage lambda DNA against restriction endonuclease EcoRII. DC-methylases E. Coli K12 and EcoRII differ in their chromatographic behaviour on phosphocellulose and capacity to form compexes with the cell DNA-adenine-methylase.