The specificity of three DNA methyltransferases M. Alw 26l, M. Eco3 1l and M. Esp 3l, Isolated from Aclnetobacter iwoffi RFL26, Eschertchia coll RFL31 and Hafnla alvel RFL3 + , respectively, was determined. All the enzymes methylate both strands of asymmetric recognition sites yielding m 5 C in the top-strand and m 6 A in the bottom-strand, as below:

5′-GTm 5 CTC 5′-GGTm 5 CTC 5′-CGTm 5 CTC 3′-Cm 6 AGAG 3′-CCm 6 AGAG 3′-GCm 6 AGAG (M. Alw 26l) (M. Eco 31l) (M. Esp 3l)

They are the first members of type lls methyltransferases that modify different types of nucleotides in the recognition sequence.