LOCALIZATION TO CHROMOSOME 7Q36,1 OF THE HUMAN XRCC2 GENE, DETERMINING SENSITIVITY TO DNA-DAMAGING AGENTS

The identification of genes controlling cellular response to DNA damag e is of considerable importance, and cell lines showing hypersensitivi ty to DNA-damaging agents can be used as vehicles to map and clone the se genes. In this study the hamster cell line irs1, showing hypersensi tivity to a number of different DNA-damaging agents, was fused to norm al human cells to complement the defect. The resultant hybrids were an alysed by Alu-PCR, chromosome painting, and with DNA markers to map th e complementing gene (named XRCC2) to a specific chromosomal region, T hese hybrids showed correction of sensitivity to both X-rays and to mi tomycin-C, and contained human chromosome 7, often as their only human component, Hybrids showing unstable retention of human chromosomes we re sub-cloned to show that loss of chromosome 7 and loss of resistance to mitomycin-C occurred concordantly. Two separate hybrids were found to have a smaller piece of chromosome 7, and specific DNA probes and microsatellite markers defined this as a contiguous region at 7q35-36, Hybrid irradiation-fusion methods were used to further reduce the siz e of the complementing genomic region and to localize the gene to an a pproximately 3-5 Mb region at 7q36.1.