Complementation Mapping in Microcell Hybrids: Localization of XRCC4 to 5q15-q21.

Microcell-mediated chromosome transfer (MMCT) offers a unique method for introducing tagged individual human chromosomes from mouse/human monochromosomal hybrids into cell lines displaying recessive mutant phenotypes. Functional analysis of the resultant microcell hybrids bearing different tagged individual human chromosomes permits identification of the complementing chromosome. Using this approach, a number of human DNA repair genes that complement DNA repair defects in Xeroderma pigmentosum, Ataxia telangiectasia, Bloom's syndrome, and rodent mutant cells have been mapped to specific chromosomes. In this paper, we present experiments performed to map a DNA double-strand break (dsb) repair gene, XRCC4, to human chromosome 5q15-q21. The introduction of human chromosome 5 into Chinese hamster mutant XR-1 cells corrected their X-ray sensitivity and DNA dsb repair deficiency. Loss of chromosome 5 and concomitant reversion to the radiosensitive phenotype confirmed the presence of XRCC4 on this chromosome. Analysis of DNA markers in radiation-resistant and -sensitive clones bearing different segments of chromosome 5 placed this gene in the region 5q15-q21. These studies demonstrate the application of MMCT technology to the genetic analysis of mutations that escape other experimental approaches.