Mechanistic studies on the repair of a novel DNA photolesion: the spore photoproduct

[formula: see text] UV irradiation of spores results in the formation of the spore photoproduct. This novel DNA photolesion is repaired in the germinating spore in a reaction catalyzed by the spore photoproduct lyase. Model studies, using a simple bispyrimidine, suggest that this repair reaction proceeds by hydrogen abstraction from C6 of the spore photoproduct followed by beta-scission of the bond linking the two pyrimidines and back hydrogen atom transfer.