The Genetic Control of X-Ray Resistance in Budding Yeast Cells

Abstract

Five X-ray-sensitive mutants were selected from 10,000 colonies arising from survivors of ultraviolet light. These were named XS5, XS6, XS7, XS8, and XS9. Mutant ${\rm X}^{{\rm s}}1$ was donated by Nakai. These mutations affect the resistant budding cell survival component of the survival curve and, in diploids, the low-dose interdivisional cell shoulder. They are of two types: Class I, in which budding cells lack resistance; and Class II, in which budding cells show reduced resistance. When crossed with one another, they show a complex complementation pattern. Gene dosage effects are seen in ${\rm X}^{{\rm s}}1$ heterozygotes, while budding but not between divisions. No direct correlation between radiation sensitivity, meiosis, and sporulation is observed; genes which influence radiation sensitivity do not affect meiotic recombination. A single mutation ( ${\rm X}^{{\rm s}}1$ or XS5) suppresses the shoulders of the survival curves of both budding haploid cells and diploid nonbudding cells.