Inhibition of bacterial DNA cytosine-5-methyltransferase by S-adenosyl-L-homocysteine and some related compounds.

S-Adenosyl-L-homocysteine and five related compounds have been evaluated as inhibitors of a DNA cytosine-5-methyltransferase. DNA methylation was assayed in cell extracts from E. coli strain J6-2 dcm+, proficient in DNA cytosine-5-methyltransferase activity, containing substrate DNA isolated from E. coli strain J6-2 dcm-, a strain deficient in DNA cytosine-5-methyltransferase. S-Adenosyl-L-homocysteine and its 7-deaza analogue, S-tubercidinylhomocysteine, were competitive inhibitors of DNA cytosine-5-methyltransferase with Ki's of 14.2 and 17.6 microM, respectively, in the above enzyme assay.