Methyltransferase that methylates adenine residues in the dsDNA sequence 5'-GATC-3' (PubMed:2180941, PubMed:3312202). May prevent degradation of viral DNA by the host restriction-modification antiviral defense system (PubMed:376871). a 2'-deoxyadenosine in DNA + S-adenosyl-L-methionine = an N(6)-methyl-2'-deoxyadenosine in DNA + H(+) + S-adenosyl-L-homocysteine Optimum pH is 6.9. Optimum temperature is between 40 and 43 degrees Celsius. Expressed early in the viral replication cycle. Belongs to the N(4)/N(6)-methyltransferase family.