Inhibition of heat tolerance and nuclear import of Gts1p by Ssa1p and Ssa2p

The Saccharomyces cerevisiae gene GTS1 is pleiotropic. GTS1 induction produces a variety of biological phenomena represented by heat tolerance. To clarify the interaction partners of Gts1p, tandem affinity purification and immunoprecipitation were performed. Ssa1p and Ssa2p, members of the 70-kDa heat-shock protein family, were identified. Co-expression of SSA1 or SSA2 inhibited Gts1p nuclear import. As compared to the wild type, the SSA1 and SSA2 double-deletion mutant showed enhancement of Gts1p-mediated heat tolerance in the stationary phase, although neither of the single deletions affected heat tolerance, irrespective of GTS1 induction. These results indicate that the heat tolerance function of Gts1p is regulated by Ssa1p and Ssa2p. Furthermore, time-dependent production of Ssa1p and Ssa2p revealed that Gts1p controls the production of Ssa1p and Ssa2p, and that the total amounts of Ssa1p and Ssa2p are important in inhibiting the unique function of Gts1p.