Hypersensitivity to heavy water: A new conditional phenotype

Wild-type strains of the yeast S. cerevisiae can grow on media containing 90% D20. Using chemical mutagenesis we obtained a number of strains that grow on H2O-containing media but not on otherwise identical media containing 90% D2O. The frequency of these D20-sensitive (ds) mutants is comparable to the frequency of conventional temperature-sensitive (ts) mutants in the same mutagenized sample, and the ds mutations are distributed over a large number of complementation groups. Furthermore, most ds mutants do not display other conditional phenotypes, such as heat, cold, or osmotic sensitivity. Conversely, of 17 cell division cycle is mutants tested, only 2 are also ds. Thus, the ds technique should be useful for producing conditional mutations in genes that are not amenable to the is and cs approaches, and also for generating alternative conditional (ds) alleles in many other genes. In addition, the ds technique should make it possible to generate conditional (ds) mutants in homeothermic animals, thereby extending the advantages of conditional phenotypes to mammalian and avian genetics.