Functional domains within FEN-1 and RAD2 define a family of structure-specific endonucleases: implications for nucleotide excision repair.

Structure-specific nucleases catalyze critical reactions in DNA replication, recombination, and repair. Recently, a structure-specific endonuclease, FEN-1, has been purified and shown to cleave DNA flap structures. Here, we describe the cloning of the murine FEN-1 gene. The nucleotide sequence of FEN-1 is highly homologous to the Saccharomyces cerevisiae genes YKL510 and RAD2. We show that YKL510 and a truncated RAD2 protein are also structure-specific endonucleases. The substrate specificity of the truncated RAD2 protein implicates branched DNA structures as important intermediates in nucleotide excision repair. The polarity of these branched DNA structures allows us to predict the placement of DNA scissions by RAD2 and RAD1/RAD10 in this reaction.