A beta subtype methylase that binds the system-specific DNA recognition site 5'-CGAAT-3' and methylates A-4 (of only 1 strand). DNA restriction requires both the Res and Mod subunits. a 2'-deoxyadenosine in DNA + S-adenosyl-L-methionine = an N(6)-methyl-2'-deoxyadenosine in DNA + H(+) + S-adenosyl-L-homocysteine Homodimer, also forms a functional restriction-competent complex with Res. Belongs to the N(4)/N(6)-methyltransferase family.