Effect of thermotolerance on heat-induced excess nuclear-associated proteins

Earlier studies reported that thermotolerance had two effects on the heat‐induced increase in nuclear‐associated proteins (NAPs); reduction in NAP levels immediately following hyperthermia and facilitation of NAP recovery to control levels. It has also been demonstrated that there are two phases of thermotolerance; one that requires newly synthesized proteins (protein synthesis dependent thermotolerance; PSDT), and another that does not (protein synthesis independent thermotolerance; PSIT). This study was designed to determine if these two phases of thermotolerance affected NAP binding in a similar or different manner. The results demonstrated that protein synthesis during thermotolerance development was not required to reduce NAP levels measured immediately following hyperthermia, but was required to facilitate NAP recovery to control levels following hyperthermia. Reducing NAP levels was the predominant mechanism by which thermotolerance protected cells from this lesion at 43.0°C while facilitated NAP recovery predominated in protecting against exposure to 45.5°C. The facilitated recovery of NAPs required only proteins synthesized following thermotolerance induction and prior to the second heat challenge. Proteins synthesized following the second heat challenge were not requisite. Finally, the processes that facilitate NAP recovery were inhibited at 3°C, suggesting that they are enzymatically mediated. © 1993 Wiley‐Liss, Inc.