[Participation of methylcobalamin in the methylation of Propionibacterium shermanii DNA].

Propionibacterium shermanii is characterized by a high content of 5-methylcytosine (5 MC). The level of 5-MC in B12-deficient cells of the culture is twice as low as in the control. The in vitro treatment of DNA isolated from the B12-deficient cells with methyl-cobalamin in the presence of the extract of control cells possessing the activity of DNA-methylase increases the content of 5-MC to the control level. No additional methylation of DNA in vitro takes place in the absence of the methylase system and in the presence of other forms of corrynoids. The methylating activity is displayed either in the presence of methionine or without it. The inhibitor of methylcobalamin, i.e. diftorchlormethyl-cobalamin, blocks methylation of DNA. Small quantities of S-adenosylmethionine are necessary for the reaction of methylation.