Selective linkage disruption in human-Chinese hamster cell hybrids: deletion mapping of the leuS, hexB, emtB, and chr genes on human chromosome 5.

Chinese hamster-human interspecific hybrid cells, which contain human chromosome 5 and express four genes linked on that chromosome, were subjected to selective conditions requiring them to retain one of the four linked genes, leuS (encoding leucyl-tRNA synthetase), but lose another, either emtB (encoding ribosomal protein S14) or chr. Cytogenetic and biochemical analyses of spontaneous segregants isolated by using these unique selective pressures have enabled us to determine the order and regional location of the leuS, hexB, emtB, and chr genes on human chromosome 5. These segregants arise primarily by terminal deletions of various portions of the long arm of chromosome 5. Our results indicate that the order of at least three of these genes is the same on human chromosome 5 and Chinese hamster chromosome 2. Thus, there appears to be extensive homology between Chinese hamster chromosome 2 and human chromosome 5, which represents an extreme example of the conservation of gene organization between very divergent mammalian species. In addition, these hybrids and selective conditions provide a very simple and quantitative means to assess the potency of various agents suspected of inducing gross chromosomal damage.