HEAT-SHOCK INHIBITS AND ACTIVATES DIFFERENT PROTEIN-DEGRADATION PATHWAYS AND PROTEINASE ACTIVITIES IN NEUROSPORA-CRASSA

In Neurospora crassa, heat shock treatment inhibits proteolytic activi ty. ATP-independent proteinases were analysed after polyacrylamide gel electrophoresis using renaturing gelatine gels. Proteinases of 24, 29 , and 130 kDa were shown to be inhibited by heat shock and were furthe r characterized as to their properties. A major part of the heat shock -induced inhibition is probably due to suppression of de novo synthesi s of proteinases as deduced from experiments with cycloheximide. Durin g several hours of recovery from heat shock, the inhibition of overall protein degradation and ATP-independent proteinases is reversed. Azoc asein assays as well as pulse-chase experiments further showed that AT P-dependent protein degradation is only slightly affected by heat shoc k. Two ATP-binding proteinases of about 60 and 160 kDa even show an in creased activity after heat shock. The degradation rate of heat shock proteins is inhibited by heat shock treatment, indicating that they ar e degraded by ATP-independent proteinases. Western blot analysis of a similar to 40-kDa degradation product of HSP70 containing its amino te rminal portion revealed a reduction in the amount of this peptide afte r heat shock.