RAD23 LINKS DNA-REPAIR TO THE UBIQUITIN PROTEASOME PATHWAY/

Rad23 is an evolutionarily conserved protein that is important for nuc leotide excision repair(1-3). A regulatory role has been proposed for Rad23 because rad23 mutants are sensitive to ultraviolet light but are still capable of incising damaged DNA(4,5). Here we show that Rad23 i nteracts with the 26S proteasome through an aminoterminal ubiquitin-li ke domain (UbL(R23)). The carboxy terminus of Rad23 binds to the Rad4 DNA repair protein and creates a link between the DNA repair and prote asome pathways. The ultraviolet sensitivity caused by deletion of the UbL(R23) domain may therefore arise from its inability to interact wit h the proteasome. The fusion proteins glutathione S-transferase (GST)- Rad23 and Rad4-haemagglutinin (HA), and the proteasome subunits Cim3 a nd Cim5, cofractionate through consecutive chromatography steps. The u biquitin-like domain of human Rad23 (UbL(HRB)) also interacts with the human proteasome. These results demonstrate that ubiquitin-like domai ns (UbLs) represent a new class of proteasome-interacting motifs.