Conformation of N6-methyladenine, a base involved in DNA modification: restriction processes.

Crystal structures of N(6),N(9)-dimethyladenine and N(6)-methyladenine hydrochloride were determined from three-dimensional x-ray diffraction data. The bases assume a conformation in which the N(6)-methyl group blocks one of the hydrogen-bonding sites normally used by adenine to form Watson-Crick pairs with thymine in double-helical DNA. When in this conformation, N(6)-methyladenine residues might alter the secondary structure of DNA. thereby preventing the scission of modified DNA's by restriction enzymes.