Characterization of the heat shock response in protoplasts of Aspergillus nidulans

Abstract

A typical heat shock response, characterized by the preferential synthesis of a select class of proteins was observed in protoplasts isolated from the mycelium of Aspergillus nidulans when shifted from 37 °C to 43° or 46°. Several prominent heat shock proteins (HSPs) were identified under different conditions of heat shock. Accumulation labelling was used to measure the onset of HSP synthesis and the accretion of these proteins over a time period. Synthesis of several proteins increased during a 60 min heat shock at 43° and some of these continued to be synthesized in protoplasts that were returned to the pre-shift temperature for up to 60 min. Pulse-labelling was used to monitor the time course of synthesis of individual heat induced polypeptides. It was apparent that the kinetics of HSP gene expression in A. nidulans is similar to that in other eukaryotes. Heat shock elicited the temporal and qualitatively different levels of expression of numerous genes under independent regulation. Following mild heat shock at 43° HSPs were synthesized at moderate levels against a background of near to normal cell synthesis. When a more severe heat shock was used constitutive synthesis of all proteins after 75 min at 46° suggests that this is approaching the lethal temperature for survival of A. nidulans.