TRANSIENT ACQUIRED THERMOTOLERANCE IN DROSOPHILA, CORRELATED WITH RAPID DEGRADATION OF HSP70 DURING RECOVERY

Acquired thermotolerance, measured either as increased cell viability following a lethal heat shock or by translational thermotolerance, app ears rapidly following a 'priming' heat treatment, but also decays rap idly. 4 hours after priming heating thermotolerance is reduced by > 50 % and by 9 hours it is virtually undetectable. Heat-shock protein 70 ( Hsp70) turns over with a half-life of approximately 2 hours, and the d ecline in its intracellular abundance parallels the loss of acquired t hermotolerance. Continuous heat shock extends the half-life of Hsp70 t o approximate to 7 hours. When Hsp70 is expressed at normal temperatur e using a metallothionein promoter, only partial acquired translationa l thermotolerance results. The results suggest that acquired thermotol erance is tightly regulated in Drosophila and partly, but not wholly, determined by post-translational regulation of Hsp70 levels.