Regulation of gene expression in Tetrahymena pyriformis under heat-shock and during recovery.

Proteins extracted from Tetrahymena pyriformis cells, which were shifted from 28 degrees C to 34 degrees C (heat-shocked) and then labelled with [35S]-methionine, were analysed by two-dimensional gel electrophoresis according to the method of O'Farrell. In the fluorogram obtained after 2.5 min heat-shock new polypeptide spots already appear in the region of 70-75 kDa and 25-29 kDa, indicating that the induction response is very rapidly triggered. Other newly induced proteins become more intense after 15 min and 30 min of heat-shock. After a 60-min treatment, the electrophoretic analysis shows the normal pattern of proteins resembling that of exponentially growing cells. Our experiments in vivo and in vitro also show that the messengers coding for stress proteins have a short lifetime, suggesting that modulation of the translation efficiency of heat-shock protein mRNAs is accompanied by an alteration in their biological stability. Studies using the inhibitor actinomycin D suggest that control of this response is exercise mainly at the transcriptional level for the 70-75-kDa and at the translational level for the 25-29-kDa heat-shock proteins. When T. pyriformis cells are allowed to recover at 28 degrees C the heat-shock proteins disappear completely and normal protein synthesis is completely re-established. Although the level of normal protein synthesis attained is lower, cells are able to recover completely from heat-shock when new mRNA synthesis is blocked by actinomycin D, indicating a conservation of normal pre-existing mRNAs during heat-shock.