Showing papers by "Susan Lindquist published in 1989"

hsp82 is an essential protein that is required in higher concentrations for growth of cells at higher temperatures.

Abstract: hsp82 is one of the most highly conserved and abundantly synthesized heat shock proteins of eucaryotic cells. The yeast Saccharomyces cerevisiae contains two closely related genes in the HSP82 gene family. HSC82 was expressed constitutively at a very high level and was moderately induced by high temperatures. HSP82 was expressed constitutively at a much lower level and was more strongly induced by heat. Site-directed disruption mutations were produced in both genes. Cells homozygous for both mutations did not grow at any temperature. Cells carrying other combinations of the HSP82 and HSC82 mutations grew well at 25 degrees C, but their ability to grow at higher temperatures varied with gene copy number. Thus, HSP82 and HSC82 constitute an essential gene family in yeast cells. Although the two proteins had different patterns of expression, they appeared to have equivalent functions; growth at higher temperatures required higher concentrations of either protein. Biochemical analysis of hsp82 from vertebrate cells suggests that the protein binds to a variety of other cellular proteins, keeping them inactive until they have reached their proper intracellular location or have received the proper activation signal. We speculate that the reason cells require higher concentrations of hsp82 or hsc82 for growth at higher temperatures is to maintain proper levels of complex formation with these other proteins.

Regulation of HSP70 synthesis by messenger RNA degradation.

Abstract: When Drosophila cells are heat shocked, hsp70 messenger RNA (mRNA) is stable and is translated at high efficiencies. During recovery from heat shock, hsp70 synthesis is repressed and its messenger RNA (mRNA) is degraded in a highly regulated fashion. Dramatic differences in the timing of repression and degradation are observed after heat treatments of different severities. The 3' untranslated region (UTR) of the hsp70 mRNA was sufficient to transfer this regulated degradation to heterologous mRNAs. Altering the translational efficiency of the message or changing its natural translation-termination site did not alter its pattern of regulation, although in some cases it changed the absolute rate of degradation. We have previously shown that hsp70 mRNA is very unstable when it is expressed at normal growth temperatures (from a metallothionein promoter). We report here that the 3' untranslated region of the hsp70 mRNA is responsible for this instability as well. We postulate that a mechanism for degrading hsp70 mRNA pre-exists in Drosophila cells, that it is inactivated by heat shock and that it is the reactivation of this mechanism that is responsible for hsp70 repression during recovery. This degradation system may be the same as that used by other unstable mRNAs.

hsp26 of Saccharomyces cerevisiae is related to the superfamily of small heat shock proteins but is without a demonstrable function.

Abstract: Analysis of the cloned gene confirms that hsp26 of Saccharomyces cerevisiae is a member of the small heat shock protein superfamily. Previous mutational analysis failed to demonstrate any function for the protein. Further experiments presented here demonstrate that hsp26 has no obvious regulatory role and no major effect on thermotolerance. It is possible that the small heat shock protein genes originated as primitive viral or selfish DNA elements.

The intracellular location of yeast heat-shock protein 26 varies with metabolism.

Abstract: An antibody highly specific for heat-shock protein (hsp)26, the unique small hsp of yeast, and mutants carrying a deletion of the HSP26 gene were used to examine the physical properties of the protein and to determine its intracellular distribution The protein was found in complexes with a molecular mass of greater than 500 kD Thus, it has all of the characteristics, including sequence homology and induction patterns, of small hsps from other organisms When log-phase cells growing in glucose were heat shocked, hsp26 concentrated in nuclei and continued to concentrate in nuclei when these cells were returned to normal temperatures for recovery However, hsp26 did not concentrate in nuclei under a variety of other conditions For example, in early stationary-phase cells hsp26 is induced at normal growth temperatures This protein was generally distributed throughout the cells, even after heat shock Similarly, in cells genetically engineered to synthesize hsp26 in the presence of galactose, hsp26 did not concentrate in nuclei, with or without a heat shock To determine if the failure of hsp26 to concentrate in the nucleus of these cells was due to the fact that the protein had been produced at 25 degrees C or to a difference in the physiological state of the cell, we investigated the distribution of the heat-induced protein in cells grown under several different conditions In wild-type cells grown in galactose or acetate and in mitochondrial mutants grown in glucose or galactose, hsp26 also failed to concentrate in nuclei with a heat shock We conclude that the intracellular location of hsp26 in yeast depends upon the physiological state of the cell and not simply upon the presence or absence of heat stress Our findings may explain why previous investigations of the intracellular localization of small hsps in a variety of organisms have yielded seemingly contradictory results