MAPPING OF INTERACTION DOMAINS BETWEEN HUMAN REPAIR PROTEINS ERCC1 AND XPF

ERCC1-XPF is a heterodimeric protein complex involved in nucleotide ex cision repair and recombinational processes. Like its homologous compl ex in Saccharomyces cerevisiae, Rad10-Rad1, it acts as a structure-spe cific DNA endonuclease, cleaving at duplex-single-stranded DNA junctio ns. In repair, ERCC1-XPF and Rad10-Rad1 make an incision on the the 5' -side of the lesion. No humans with a defect in the ERCC1 subunit of t his protein complex have been identified and ERCC1-deficient mice suff er from severe developmental problems and signs of premature aging on top of a repair-deficient phenotype. Xeroderma pigmentosum group F pat ients carry mutations in the XPF subunit and generally show the clinic al symptoms of mild DNA repair deficiency. All XP-F patients examined demonstrate reduced levels of XPF and ERCC1 protein, suggesting that p roper complex formation is required for stability of the two proteins. To better understand the molecular and clinical consequences of mutat ions in the ERCC1-XPF complex, we decided to map the interaction domai ns between the two subunits. The XPF-binding domain comprises C-termin al residues 224-297 of ERCC1, Intriguingly, this domain resides outsid e the region of homology with its yeast Rad10 counterpart. The ERCC1-b inding domain in XPF maps to C-terminal residues 814-905. ERCC1-XPF co mplex formation is established by a direct interaction between these t wo binding domains. A mutation from an XP-F patient that alters the ER CC1-binding domain in XPF indeed affects complex formation with ERCC1.