The mutagenic effect of elevated temperatures in yeast is blocked by a previous heat shock.

We have analyzed the mutagenic effect of elevated temperatures (hyperthermia: HT) either upon direct exposure or after a previous heat shock (HS) in the haploid auxotrophic Saccharomyces cerevisiae strain SC7K lys2-3 in the logarithmic phase of growth. We demonstrated a significant antimutagenic effect of HS (38 degrees C for 1 h) followed by hyperthermia (48 degrees C, up to 60 min). Using cycloheximide (CHM) during the HS exposure we reversed the antimutagenic effect. We suggest that, upon HS, the enzymes involved in repair of premutational damage are more resistant to denaturation, i.e., by the induced HSP genes, and could work efficiently to prevent damage fixation in critical targets. CHM blocks the antimutagenic effect of the HS treatment by inhibiting the inducible synthesis of HSP.