The stress response against denatured proteins in the deletion of cytosolic chaperones SSA1/2 is different from heat-shock response in Saccharomyces cerevisiae

Graduate School of Science and Technology, Chiba University, Inage, Chiba 263-8522, Japan.
BMC Genomics (Impact Factor: 3.99). 02/2005; 6(1):141. DOI: 10.1186/1471-2164-6-141
Source: PubMed


A yeast strain lacking the two genes SSA1 and SSA2, which encode cytosolic molecular chaperones, acquires thermotolerance as well as the mild heat-shocked wild-type yeast strain. We investigated the genomic response at the level of mRNA expression to the deletion of SSA1/2 in comparison with the mild heat-shocked wild-type using cDNA microarray.
Yeast cDNA microarray analysis revealed that genes involved in the stress response, including molecular chaperones, were up-regulated in a similar manner in both the ssa1/2 deletion mutant and the mild heat-shocked wild-type. Genes involved in protein synthesis were up-regulated in the ssa1/2 deletion mutant, but were markedly suppressed in the mild heat-shocked wild-type. The genes involved in ubiquitin-proteasome protein degradation were also up-regulated in the ssa1/2 deletion mutant, whereas the unfolded protein response (UPR) genes were highly expressed in the mild heat-shocked wild-type. RT-PCR confirmed that the genes regulating protein synthesis and cytosolic protein degradation were up-regulated in the ssa1/2 deletion mutant. At the translational level, more ubiquitinated proteins and proteasomes were detected in the ssa1/2 deletion mutant, than in the wild-type, confirming that ubiquitin-proteasome protein degradation was up-regulated by the deletion of SSA1/2.
These results suggest that the mechanism for rescue of denatured proteins in the ssa1/2 deletion mutant is different from that in the mild heat-shocked wild-type: Activated protein synthesis in the ssa1/2 deletion mutant supplies a deficiency of proteins by their degradation, whereas mild heat-shock induces UPR.

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Available from: Randeep Rakwal
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    • "A previous study comparing the global gene expression changes in yeast upon mild heat shock to those for yeast cells deleted for both SSA1 and SSA2, identified differential expression of groups of genes that are very distinct from those identified in our analysis [70]. Significant differences in strain background and SSA deletion status exists between these studies and therefore a direct comparison between global gene expression data is not possible. "
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