An alpha subtype methylase that recognizes the double-stranded sequence 5'-GGATG-3' in one strand and 3'-CATCC-5' in the other, methylates A of both strands, and protects the DNA from cleavage by the StsI endonuclease. The 2 domains of the protein participate in modification of the two strands. a 2'-deoxyadenosine in DNA + S-adenosyl-L-methionine = an N(6)-methyl-2'-deoxyadenosine in DNA + H(+) + S-adenosyl-L-homocysteine Monomer. Belongs to the N(4)/N(6)-methyltransferase family.