AN INTERACTION BETWEEN THE DNA-REPAIR FACTOR XPA AND REPLICATION PROTEIN-A APPEARS ESSENTIAL FOR NUCLEOTIDE EXCISION-REPAIR

Replication protein A (RPA) is required for simian virus 40-directed D NA replication in vitro and for nucleotide excision repair (NER). Here we report that RPA and the human repair protein XPA specifically inte ract both in vitro and in vivo. Mapping of the RPA-interactive domains in XPA revealed that both of the largest subunits of RPA, RPA-70 and RPA-34, interact with XPA at distinct sites. A domain involved in medi ating the interaction with RPA-70 was located between XPA residues 153 and 176. Deletion of highly conserved motifs within this region ident ified two mutants that were deficient in binding RPA in vitro and high ly defective in NER both in vitro and in vivo. A second domain mediati ng the interaction with RPA-34 was identified within the first 58 resi dues in XPA. Deletion of this region, however, only moderately affects the complementing activity of XPA in vivo. Finally, the XPA-RPA compl ex is shown to have a greater affinity for damaged DNA than XPA alone. Taken together, these results indicate that the interaction between X PA and RPA is required for NER but that only the interaction with RPA- 70 is essential.