Mechanism of DNA strand nicking at apurinic/apyrimidinic sites by Escherichia coli [formamidopyrimidine]DNA glycosylase

Abstract
Escherichia coli [formamidopyrimidine]DNA glycosylase catalyses the nicking of both the phosphodiester bonds 3'' and 5'' of apurinic or apyrimidinic sites in DNA so that the base-free deoxyribose is replaced by a gap limited by 3''-phosphate and 5''-phosphate ends. The two nickings are not the results of hydrolytic processes; the [formamidopyrimidine]DNA glycosylase rather catalyses a .beta.-elimination reaction that is immediately followed by a .delta.-elimination. The enzyme is without action on a 3''-terminal base-free deoxyribose or on a 3''-terminal base-free unsaturated sugar produced by a .beta.-elimination reaction nicking the DNA strand 3'' to an apurinic or apyrimidinic site.