RAD6 gene is involved in heat shock induction of bleomycin resistance in Saccharomyces cerevisiae

Cells react to environmental and endogenous challenges such as high temperature, reactive oxygen species, DNA damage, and nutrient starvation by activating several defense mechanisms known as stress responses. An important feature is the overlap between different stress responses that contributes at least in part to the phenomenon of cross-protection. We previously demonstrated that pretreatment with a heat shock (HS) induces resistance to the lethal and mutagenic effects of the antineoplastic drug Bleomycin (BLM) in wild-type Saccharomyces cerevisiae. At the DNA level, the HS resulted in more efficient repair of BLM-induced DNA damage. In the present study, we have investigated the mechanisms involved in this HS-induced BLM resistance. Since the RAD6 gene is involved in the ubiquitin system and DNA repair, we analyzed the effects of HS on the lethality of BLM in a rad6Delta (ubc2) mutant strain of S. cerevisiae. The rad6Delta mutant was more sensitive to the lethal effects of BLM than wild-type yeast and HS had no effect on the lethality of BLM in the mutant. Analysis of cell proliferation kinetics indicated that the HS-induced cell cycle delay observed in the wild-type yeast was absent in the rad6Delta mutant strain. BLM treatment impaired mutant cell proliferation, and HS had no effect on the delayed cell kinetics of the mutant. In addition, pulsed-field electrophoresis of chromosomes damaged by BLM indicated that there was very little recovery from damage in the mutant after 24 hr of incubation in BLM-free nutrient medium, and that HS had little effect on the recovery. These data indicate that the RAD6 gene is involved in the HS-induced BLM resistance observed in the isogenic wild-type strain.