A eukaryotic DNA glycosylase/lyase recognizing ultraviolet light-induced pyrimidine dimers.

Cyclobutane pyrimidine dimers (CPDs) are the predominant product of photodamage in DNA after exposure of cells to ultraviolet light and are cytotoxic, mutagenic and carcinogenic in a variety of cellular and animal systems. In prokaryotes, enzymes and protein complexes have been characterized that remove or reverse CPDs in DNA. Micrococcus luteus and T4 phage-infected Escherichia coli contain a specific N-glycosylase/apurinic-apyrimidinic lyase that catalyses a two-step DNA incision process at sites of CPDs, thus initiating base excision repair of these lesions. It is well established that CPDs are recognized and removed from eukaryotic DNA by excision repair processes but very little information exists concerning the nature of the proteins involved in CPD recognition and DNA incision events. We report here that an enzyme functionally similar to the prokaryotic N-glycosylase/apurinic-apyrimidinic lyases exists in Saccharomyces cerevisiae. To our knowledge, this is the first time such an activity has been found in a eukaryote and is also the first example of an organism having both direct reversal and base excision repair pathways for the removal of CPDs from DNA.