Altered patterns of protein synthesis induced by heat shock of yeast

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Abstract
The products of protein synthesis from exponential phase cultures of Saccharomyces cerevisiae grown at 23 °C or at 36 °C appear to be essentially identical. However, yeast cells respond to a shift in culture temperature from 23 °C to 36 °C with the rapid de novo synthesis of a polypeptide species of molecular weight 100,000. Within 60–90 min after the shift this polypeptide represents approximately 2.5% of the total cellular protein, a 5–10 fold increase over the preshift level. The level of this polypeptide then decreases with continued growth of the cells at 36 °C. Analyses by SDS-polyacrylamide gel electrophoresis of polypeptides obtained from cells pulse labeled with [35S]methionine demonstrate that following a temperature shift from 23 °C to 36 °C the synthetic rate of the 100,000 molecular weight polypeptide (as well as a number of other polypeptide species) increases to a level at least 10 fold higher than that observed prior to the shift. A concomittant decrease is observed in the synthesis of a large number of polypeptide species which were actively synthesized before the shift. Maximum changes in synthetic rates are observed 20–30 min after the shift and preshift synthetic patterns are regained within 60–90 min. Synthetic changes of the same magnitude and time course can be produced by short (20–30 min) exposures to 36 °C implicating a heat shock response. Several of the transiently induced polypeptides, including the 100,000 molecular weight species, show an affinity for DNA as determined by DNA-cellulose chromatography.