Photolysis of methylated DNA

Abstract

We have compared the photochemical reactivity at 254 and 280 nm of naturally occurring 5-methylcytosine (m 5 C) residues in DNA to that of thymine (T) residues in DNA. The m 5 C residues yielded less photoproduct than did T residues, especially at 280 nm. Little or no formation of cyclobutane-type pyrimidine photodimers from the m 5 C residues was evident in contrast to the high yield of this type of photoproduct from T residues.