Induction of the Unfolded Protein Response at High Temperature in Saccharomyces cerevisiae
Tatsuya Hata; Yuki Ishiwata-Kimata; Yukio Kimata
Ire1 is an endoplasmic reticulum (ER)-located endoribonuclease that is activated in response to ER stress. In yeast Saccharomyces cerevisiae cells, Ire1 promotes HAC1-mRNA splicing to remove the intron sequence from the HAC1u mRNA (&ldquo:u&rdquo: stands for &ldquo:uninduced&rdquo:). The resulting mRNA, which is named HAC1i mRNA (&ldquo:i&rdquo: stands for &ldquo:induced&rdquo:), is then translated into a transcription factor that is involved in the unfolded protein response (UPR). In this study, we designed an oligonucleotide primer that specifically hybridizes to the exon-joint site of the HAC1i cDNA. This primer allowed us to perform real-time reverse transcription-PCR to quantify HAC1i mRNA abundance with high sensitivity. Using this method, we detected a minor induction of HAC1-mRNA splicing in yeast cells cultured at their maximum growth temperature of 39 °:C. Based on our analyses of IRE1-gene mutant strains, we propose that when yeast cells are cultured at or near their maximum growth temperature, protein folding in the ER is disturbed, leading to a minor UPR induction that supports cellular growth.
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