Abstract
We previously reported that the GTS1 product, Gts1p, plays an important role in the regulation of heat tolerance of yeast under glucose-limited conditions in either batch or continuous culture. Here we show that heat tolerance was decreased in GTS1-deleted and increased in GTS1-overexpressing cells under glucose-derepressed conditions during the batch culture and that the disruption of SNF1, a transcriptional activator of glucose-repressible genes, diminished this effect of GTS1. Intracellular levels of Hsp104 and trehalose, which were reportedly required for the acquisition of heat tolerance in the stationary phase of cell growth, were affected in both GTS1 mutants roughly in proportion to the gene dosage of GTS1, whereas those of other Hsps were less affected. The mRNA levels of genes for Hsp104 and trehalose-6-phosphate synthase 1 changed as a function of GTS1 gene dosage. The Q-rich domain of Gts1p fused with the DNA-binding domain of LexA activated the transcription of the reporter gene LacZ, and Gts1p lacking the Q-rich domain lost the activation activity of HSP104 and TPS1. Furthermore, Gts1p bound to subunits of Snf1 kinase, whereas it did not bind to DNA. Therefore, we suggested that GTS1 increases heat tolerance by mainly activating Snf1 kinase-dependent derepression of HSP104 and TPS1 in the stationary phase of yeast growth.
Highlights
We reported that the GTS1 gene shows pleiotropic effects on yeast in batch cultures, including the effect on heat tolerance as a function of gene dosage [1]; overexpression of GTS1 increases and deletion of GTS1 decreases the heat tolerance of yeast in the stationary phase of growth, whereas no such effects were found in exponentially growing cells
We found that heat tolerance was affected depending on the GTS1 gene dosage under derepressed conditions and that Gts1p acts as a transcriptional activator for HSP104 and TPS1 depending on Snf1 kinase
We showed that Gts1p induced the acquisition of heat tolerance of yeast in the stationary phase by activating the transcription of HSP104 and TPS1 genes, depending on the presence of Snf1 kinase
Summary
Heat shock proteins; GFP, green fluorescent protein; GST, glutathione S-transferase; DAPI, 4Ј,6Ј-diamidino-2-phenylindole; SC, synthetic medium; ORF, open reading frame. This paper is available on line at http://www.jbc.org tant for TPS1 and HSP104 showed severe heat sensitivity in the stationary phase [21]. We investigated the mechanism by which Gts1p modulates the acquisition of heat tolerance in yeast during the stationary phase of cell growth. We found that heat tolerance was affected depending on the GTS1 gene dosage under derepressed conditions and that Gts1p acts as a transcriptional activator for HSP104 and TPS1 depending on Snf kinase. We further showed that the carboxyl-terminal Q-rich domain of Gts1p is essential for the transcriptional activation, whereas the protein lacks DNA binding activity
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