A NEW CLASS OF DNA GLYCOSYLASE APURINIC APYRIMIDINIC LYASES THAT ACT ON SPECIFIC ADENINES IN SINGLE-STRANDED-DNA/

Although the biological function of DNA glycosylases is to protect the genome by removal of potentially cytotoxic or mutagenic bases, this i nvestigation describes the existence of natural DNA glycosylases with activity on undamaged, nonmispaired bases. Gelonin, pokeweed antiviral protein, and ricin, previously described as ribosome-inactivating pro teins, are shown to damage single-stranded DNA by removal of a protein -specific set of adenines and cleavage at the resulting abasic sites. Using an oligonucleotide as the substrate reveals that the reaction pr oceeds via the enzyme-DNA imino intermediate characteristic of DNA gly cosylase/AP lyases. The adenine glycosylase activity on single-strande d DNA reported here challenges the concept that a normal base has to b e in a mismatch to be specifically removed. By contrast to other glyco sylases, these enzymes are expected to damage DNA rather than particip ate in repair processes. The significance of this DNase activity to th e biological function of these plant proteins and to their toxicity to animal cells remains to be determined.