HEAT-SHOCK INDUCTION OF IONIZING-RADIATION RESISTANCE IN SACCHAROMYCES-CEREVISIAE - TRANSIENT CHANGES IN GROWTH-CYCLE DISTRIBUTION AND RECOMBINATIONAL ABILITY

While excision-defective mutants respond like the wild type, recombination-deficient mutants do not display the 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 increased 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 2 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. Heat-shock induction of radiation resistance in wild-type diploid yeast results from at least 2 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. Heat-shock induction of thermal resistance proceeds by an independent mechanism.