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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    • "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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    • "A. fumigatus has evolved mechanisms to thrive under these conditions, and is considered one of the most thermotolerant species of mold [43]. Since elevated temperatures induce conformational changes in proteins [44], an increase in temperature is likely to engage pathways that are relevant to ER stress response. We therefore compared the translational efficiency of A. fumigatus mRNAs at 25°C, representing the environment, to that of mRNAs following a shift to 37°C, reflecting adaptation to the mammalian host. "
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    • "Despite the considerable attention given to heat-shock regulation (for a review, see Morano et al. 2012), less is known about the cellular functions that are required to maintain resistance to a sudden heat shock. There have been several transcriptomic analyses of how yeast cells respond to various forms of heat shock (Gasch et al. 2000; Causton et al. 2001; Segal et al. 2003; Matsumoto et al. 2005), and a genome-wide analysis of gene promoters that bind the heat-shock factor (Hahn et al. 2004). However, major differences exist between genes whose expression is altered in response to a given stress vs. those needed for resistance to the stress (Giaever et al. 2002; Thorpe et al. 2004; Berry and Gasch, 2008; Mitchell et al. 2009). "
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