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