Abstract
BackgroundA 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.ResultsYeast 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.ConclusionThese 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.
Highlights
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
Comparison of the mRNA expression profiles between the ssa1/2 deletion mutant and the mild heat-shocked wildtype To investigate the mechanism of the response to denatured proteins comprehensively, the mRNA expression profiling of the ssa1/2 deletion mutant was carried out using yeast cDNA microarray, in comparison with the mild heat-shocked wild-type
Results from cDNA microarray analysis reveal that the stress-inducible protein genes, including molecular chaperones, were up-regulated in the ssa1/2 deletion mutant in a similar fashion as seen in the mild heat-shocked wildtype (Figs. 1A, 2A, and 5B)
Summary
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. Exposure to certain kinds of environmental stress factors, such as chemical, heat, osmotic, etc., induces living organisms to express stress proteins, thereby enabling the organism to acquire stress tolerance This phenomenon is called the "stress response". There is no change in the phenotype of deletion in either of the SSA1 and SSA2 genes compared with the wild-type They do not show thermotolerance without pre-heat treatment at 37°C [14]. A suppressor, EXA3-1 which is an allele of HSF1 encoding a heat shock factor [15,16] recovers its growth rate This phenomenon in the ssa1/2 deletion mutant is speculated to result from the overexpression of certain Hsps [17]. HSP104 and SSA4 are found to be highly expressed in the ssa1/2 deletion mutant [4,18]
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