The effects of low dose 60Co-gamma-radiation on radioresistance, mutagenesis, gene conversion, cell cycle and transcriptome profile in Saccharomyces cerevisiae

The underlying principles of low (stress)-dose Radiation-Induced Radioresistance (RIR) are inadequately understood. The present investigation focuses on understanding the genetic basis of RIR in Saccharomyces cerevisiae. In comparison with non-pre-irradiated cultures, the cultures that were pre-irradiated with a low dose of 60Co γ-radiation showed increased survivors (32%) but decreased convertants (26%) and revertants (65%) after irradiation with a lethal dose of 60Co γ-radiation. The radioresistance was higher if the stress dose was delivered at lower dose rate. The prolonged S-phase upregulation of genes from clusters of signal transduction, DNA damage repair, stress response, cell cycle and energy generation and down-regulation of genes from Unfolded Protein Response (UPR) pathways were observed in stress-dose irradiated cells when studied with the microarray technique. The post-irradiation variations in Heat Shock Proteins (HSPs) and the Mre11-Rad50-Xrs2 (MRX) complex were time-dependent and confirmed by real-time Quantitative-Polymerase Chain Reaction (Q-PCR) and Western blotting. This study suggests a combined role of HSPs and the MRX complex in RIR.