ISOLATION AND CHARACTERIZATION OF MOUSE XRCC-1, A DNA-REPAIR GENE AFFECTING LIGATION

Human DNA repair gene XRCC1 complements the strand-break rejoining def ect in Chinese hamster mutant EM9 and encodes a protein that is appare ntly required for optimal activity of DNA ligase III. Toward the goal of producing transgenic mice that carry a mutation in the Xrcc-1 locus , the murine homolog of XRCC1 was cloned from both cosmid genomic and cDNA libraries. Upon transfection into EM9 cells, cosmids containing t he functional mouse gene efficiently corrected (94-100%) the high sist er-chromatid-exchange defect. Mouse Xrcc-1 is 26 kb in length, contain s 17 exons, and maps by metaphase in situ hybridization to the 7A3-7B2 region of mouse chromosome 7. Isolated cDNA clones were highly trunca ted and were extended by anchored polymerase chain reactions. The 1893 -bp open reading frame of mouse Xrcc-1 encodes 631 amino acids, compar ed with 633 for the human homolog. The predicted mouse Xrcc-1 protein of 69.1 kDa and pI of 5.95 is 86% identical and 93% similar to human X RCC1. (C) 1994 Academic Press, Inc.