Quantitative analysis of the heat shock response of Saccharomyces cerevisiae

Transient protein synthesis in Saccharomyces cerevisiae, after shift from 21-23 degrees C to 37 degrees C, was quantitatively analyzed. Pulse-labeled proteins were separated by two-dimensional gel electrophoresis, and autoradiograms of the gels were analyzed by a recently described method involving a computer-coupled film scanning system. In this way, the rate of incorporation of L-[35S]methionine into approximately 500 proteins was followed. The synthesis of more than 80 of these proteins was transiently induced at 37 degrees C, with about 20 being classified as major heat shock proteins (defined as those whose rate of labeling was increased at least eightfold at some time during the response). The synthesis of more than 300 of the proteins was transiently repressed at 37 degrees C, and several general temporal patterns of repression could be distinguished. The influence of temperature-sensitive mutations affecting RNA synthesis and transport on the heat shock response was also examined. A protein whose induction in response to heat shock has a post-transcriptional component could be identified. As previously pointed out, the heat shock repression of certain proteins is so rapid that it also must involve post-transcriptional effects.