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 damage is of considerable importance, and cell lines showing hypersensitivity to DNA-damaging agents can be used as vehicles to map and clone these genes. In this study the hamster cell line irs1, showing hypersensitivity to a number of different DNA-damaging agents, was fused to normal human cells to complement the defect. The resultant hybrids were analysed by Alu-PCR, chromosome painting, and with DNA markers to map the complementing gene (named XRCC2) to a specific chromosomal region. These hybrids showed correction of sensitivity to both X-rays and to mitomycin-C, and contained human chromosome 7, often as their only human component. Hybrids showing unstable retention of human chromosomes were 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 size of the complementing genomic region and to localize the gene to an approximately 3-5 Mb region at 7q36.1.