CHARACTERIZATION OF THE MOUSE HOMOLOG OF THE XPBC/ERCC-3-GENE IMPLICATED IN XERODERMA-PIGMENTOSUM AND COCKAYNES-SYNDROME

The human XPBC/ERCC-3 DNA repair gene specifically corrects the repair defect of xeroderma pigmentosum (XP) complementation group B and rodent repair mutant cell lines of group 3. The gene encodes a presumed DNA- and chromatin-binding helicase involved in early steps of the excision repair pathway. To study the evolution of this gene, its expression in different tissues and stages of development and to permit the generation of a mouse model of XP by targeted gene replacement in mouse embryonal stem cells, we have isolated the mouse XPBC/ERCC-3 homolog. Sequence comparison of the predicted protein revealed a 96% amino acid identity with the human gene product. Notably, all postulated functional domains were strictly conserved. The mouse XPBC/ERCC-3 promoter is-like its human counterpart-devoid of classical promoter elements such as TATA and CAAT boxes and contains several conserved segments with unknown function. One of these conserved regions, consisting in part of a polypyrimidine track, is also present in the ERCC-1 promoter. The mouse XPBC/ERCC-3 gene is expressed constitutively at low levels in all tissues examined except for testis, where its expression is significantly enhanced.