Using dA methylase (DAM) (New England Biolabs, M0222), a methyl group was added to the adenine (N6) in every 5′-GATC-3′ sequence. One microgram of DNA, 1× methyltransferase reaction buffer, 80 μM S-adenosylmethionine, 1 μl of DAM, and distilled water in 10 μl were incubated at 37°C for 1 hour, followed by 65°C for 15 min. The reaction was scaled up as needed. To control for successful methylation, 500 ng of DNA were digested with either Dpn I (New England Biolabs, R0176) or Mbo I (New England Biolabs, R0147) at 37°C for 15 min. Dpn I cuts at 5′-GATC-3′ if 6mdA is present, while Mbo I cuts the same sequence in the absence of adenine methylation. The resulting products were run on a 1% agarose gel.