The genetic basis of resistance to ionising radiation damage in cultured mammalian cells.

To test the genetic similarity of independently-isolated hamster cell mutants sensitive to ionising radiation, these were fused in pairs and the hybrids exposed to X-rays. Some mutants (irs1, irs3, xrs-1, XR-1, BLM2) were found to complement all others tested for radiosensitivity in hybrids, and are therefore in separate genetic groups. The mutants irs2 and V-E5, both isolated from V79 cells, did not complement and therefore belong to the same group. Another pair, EM7 and irs1SF, formed hybrids with intermediate levels of survival between mutant and wild-type. However, the parental cells fused to irs1SF also showed intermediate sensitivity, suggesting a semi-dominant mutant phenotype rather than a lack of complementation. Crosses of some of these hamster mutants to the radiosensitive mouse mutant M10 showed clear complementation (irs1 x M10, irs2 x M10) but for others the complementation did not greatly exceed the sensitivity of one (irs3 x M10) or both mutants (XR-1 x M10). Taken with our previously-published data, these results show that there are at least 8 genetic groups determining resistance to ionising radiation damage in rodent cells.