CORRECTION OF CHROMOSOMAL INSTABILITY AND SENSITIVITY TO DIVERSE MUTAGENS BY A CLONED CDNA OF THE XRCC3 DNA-REPAIR GENE

The mutagen-sensitive CHO line irs1SF was previously isolated on the b asis of hypersensitivity to ionizing radiation and was found to be chr omosomally unstable as well as cross-sensitive to diverse kinds of DNA -damaging agents. The analysis of somatic cell hybrids formed between irs1SF and human lymphocytes implicated a human gene (defined as XRCC3 ; x-ray repair cross-complementing), which partially restored mitomyci n C resistance to the mutant. A functional cDNA that confers mitomycin C resistance was transferred to irs1SF cells by transforming them wit h an expression cDNA library and obtaining primary and secondary trans formants. Functional cDNA clones were recovered from a cosmid library prepared from a secondary transformant. Transformants also showed part ial correction of sensitivity to cisplatin and gamma-rays, efficient c orrection of chromosomal instability, and substantially improved plati ng efficiency and growth rate. The XRCC3 cDNA insert is approximate to 2.5 kb and detects an approximate to 3.0-kb mRNA on Northern blots, T he cDNA was mapped by fluorescence in situ hybridization to human chro mosome 14q32.3, which was consistent with the chromosome concordance d ata of two independent hybrid clone panels.