TRANSCRIPTIONAL AND TRANSLATIONAL REGULATION OF MAJOR HEAT-SHOCK PROTEINS AND PATTERNS OF TREHALOSE MOBILIZATION DURING HYPERTHERMIC RECOVERY IN REPRESSED AND DEREPRESSED SACCHAROMYCES-CEREVISIAE

Patterns of heat shock gene transcription and translation, as well as trehalose content, were investigated in both glucose (repressed) and a cetate (derepressed) grown cells of Saccharomyces cerevisiae during he at shock and subsequent return of cells to 25 degrees C. Heat-shocked cells (37 degrees C for 30 min), grown in either glucose- or acetate-s upplemented media, initially acquired high thermotolerance to a 50 deg rees C heat stress, which was progressively lost when cultures were al lowed to recover at 25 degrees C and subsequently exposed to a second heat stress. In all cases, with the notable exception of repressed cel ls of a relatively thermosensitive strain, inhibition of protein synth esis and coincident decrease in trehalose accumulation during the heat shock had little effect on the kinetics of loss of thermotolerance. H ear shock at 37 degrees C elicited a marked increase in transcription and translation of genes encoding major heat shock proteins (hsps). Du ring recovery at 25 degrees C, both metabolic activities were suppress ed followed by a gradual increase in hsp mRNA transcription to levels observed prior to heat shock. De novo translation of hsp mRNAs, howeve r, was no longer observed during the recovery phase, although immunode tection analyses demonstrated persistence of high levels of hsps 104, 90, 70, and 60 in cells throughout the 240-min recovery period. In add ition, while heat shock induced trehalose was rapidly degraded during recovery in repressed cells, levels remained high in derepressed cells . Results therefore indicated that the progressive loss of induced the rmotolerance exhibited by glucose- and acetate-grown cells was not clo sely correlated with levels of hsp or trehalose. It was concluded that both constitutive and de novo synthesized hsps require heat shock ass ociated activation to confer thermotolerance and this modification is progressively reversed upon release from the heat-shocked state.