The RAD23 gene of Saccharomyces cerevisiae is required for excision-repair of UV damaged DNA (1). RAD23 resembles the other DNA repair genes, RAD2, RAD6, RAD7, RAD18, and RAD54, all of which also exhibit increased transcription in response to DNA damage and during meiosis (2). RAD23 encodes a nuclear protein containing a ubiquitin-like domain required for biological function (3). RAD23 bears a ubiquitin-like domain at its amino terminus and this ubiquitin-like domain affects protein function in a nonproteolytic manner (3). Rad23 is a highly conserved protein involved in nucleotide excision repair (NER) that associates with the proteasome via its amino-terminus (4). Its carboxy-terminal ubiquitin-associated domain is evolutionarily conserved from yeast to humans (4). In addition to a role in DNA repair events in yeast, several lines of evidence indicate that the Rad23 protein may regulate the activity of the 26 S proteasome (5).