Heat-Shock Induction of Ionizing Radiation Resistance in Saccharomyces cerevisiae. Transient Changes in Growth Cycle Distribution and Recombinational Ability

Abstract

MITCHEL, R. E. J., AND MORRISON, D. P., Heat-Shock Induction of Ionizing Radiation Resistance in Saccharomyces cerevisiae. Transient Changes in Growth Cycle Distribution and Recombinational Ability. Radiat. Res. 92, 182-187 (1982). We have shown previously that a heat shock induces a transient increase in the resistance of wild-type Saccharomyces cerevisiae to the lethal effects of ionizing radiation. This increase was similar to the increase in resistance to thermal killing induced by the same heat shock, but appeared at a slightly earlier time after the temperature increase. We now show that while excision-defective mutants respond like the wild type, recombination-deficient mutants do not display this heat-shock induction of radiation resistance, but still show induction of thermal resistance. The maximum ability for recombinational repair after a heat shock was measured directly (by gene conversion) in wild-type diploids and was found to increase transiently with kinetics very similar to the increase in resistance to the lethal effects of a single dose of radiation. Radiation survival curves of wild-type cells exposed to the elevated temperature were able to resolve two populations of cells on the basis of their sensitivity to ionizing radiation. Following a heat shock, the proportion of resistant cells increased temporarily in parallel with the increase in radiation resistance. We conclude that heat-shock induction of radiation resistance in wild-type diploid yeast results from at least two changes, an increase in recombinational repair capacity, possibly associated with G1 cells, and a shift in population distribution to a higher fraction of resistant cells. We further conclude that heat-shock induction of thermal resistance proceeds by an independent mechanism.