Formation of a thymine photoproduct in transforming DNA by near ultraviolet irradiation.

Irradiation at 334 and 365 nm of a highly purified preparation of thymine-labeled transforming DNA from Haemophilus influenzae produced a photo product containing label from thymine but different from the cyclobutane dimer. The photoproduct is soluble in water and in ethanol and Rf values in a number of solvents are presented. The photoproduct has properties similar in a number of respects to those of the spore photoproduct, 5-thyminyl-5,6-dihydrothymine. The near ultraviolet photoproduct is more likely to affect the oxygen independent inactivation of transforming DNA rather than its mutagenesis, as judged by the quantitative relationship between amount of photboproduct and inactivation and mutagenesis.