Influence of relative humidity on the photochemistry of DNA films

Abstract

1. 1. Films of DNA were equilibrated at various relative humidities and then were irradiated with ultraviolet light at 25° so that changes in their photochemistry might be correlated with known conformational changes. 2. 2. Above 65% relative humidity the photochemical behavior of the films was the same as that in solution, with pyrimidine dimers, but few if any spore photoproducts, being formed. 3. 3. Below 65% relative humidity there was a 2-fold reduction in the yield of thymine dimers and a concomitant increase in the yield of spore photoproducts. 4. 4. These photochemical changes are consistent with the known conformational change in DNA films from the B form to a disorganized form as the relative humidity is reduced.