The protein encoded by this gene is one of two human homologs of Saccharomyces cerevisiae Rad23, a protein involved in nucleotide excision repair. Proteins in this family have a modular domain structure consisting of an ubiquitin-like domain (UbL), ubiquitin-associated domain 1 (UbA1), XPC-binding domain and UbA2. The protein encoded by this gene plays an important role in nucleotide excision repair and also in delivery of polyubiquitinated proteins to the proteasome. Alternative splicing results in multiple transcript variants encoding multiple isoforms.