A beta subtype methylase, recognizes the double-stranded sequence 5'-GATC-3', methylates A-2 on both strands, and protects the DNA from cleavage by the LlaDCHI endonuclease. a 2'-deoxyadenosine in DNA + S-adenosyl-L-methionine = an N(6)-methyl-2'-deoxyadenosine in DNA + H(+) + S-adenosyl-L-homocysteine The LlaDCHI restriction system has two different methylases. Genes encoded on plasmid pSQR700 confer strong resistance to the three most common lactococcal phage species (936, c2, and P335). Its presence is probably one reason for the strong bacteriophage resistance shown by strain DCH-4 over the years. Belongs to the N(4)/N(6)-methyltransferase family.