Yeast chaperone Hsp104 controls gene expression at the posttranscriptional level

Yeast chaperone Hsp104 is known as a protein responsible for dissociation of aggregates of heat-damaged proteins and prion aggregates into smaller pieces or monomers. The effects of Hsp104 on PrP-GFP and GFP were analyzed. PrP-GFP forms high-molecular-weight aggregates, whereas GFP is unable to aggregate in yeast cells. Hsp104 proved to regulate the amount of PrP-GFP and GFP in yeast cells, and the direction of chaperone action depended on the promoters controlling the production of these proteins. Overproduction of Hsp104 increased the levels of PrP-GFP and GFP when their genes were controlled by the CUP1 promoter. In contrast, overproduction of Hsp104 decreased the levels of PrP-GFP and GFP in the case of their expression under the control of the GPD promoter. The effects of Hsp104 were not related to any changes in the contents of mRNAs of the genes under investigation nor to the ability of the proteins to form aggregates. Thus, the Hsp104 functions were not confined to dissociation of protein aggregates. Hsp104 was assumed to regulate gene expression at the posttranscriptional level.