CHARACTERIZATION OF THE HEAT-SHOCK RESPONSE IN PROTOPLASTS OF ASPERGILLUS-NIDULANS

A typical heat shock response, characterized by the preferential synth esis of a select class of proteins, was observed in protoplasts isolat ed from the mycelium of Aspergillus nidulans when shifted from 37 degr ees C to 43 degrees or 46 degrees. Several prominent heat shock protei ns (HSPs) were identified under different conditions of heat shock. Ac cumulation labelling was used to measure the onset of HSP synthesis an d the accretion of these proteins over a time period. Synthesis of sev eral proteins increased during a 60 min heat shock at 43 degrees and s ome of these continued to be synthesized in protoplasts that were retu rned to the pre-shift temperature for up to 60 min. Pulse-labelling wa s used to monitor the time course of synthesis of individual heat indu ced polypeptides. It was apparent that the kinetics of HSP gene expres sion in A. nidulans is similar to that in other eukaryotes. Heat shock elicited the temporal and qualitatively different levels of expressio n of numerous genes under independent regulation. Following mild heat shock at 43 degrees 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 degrees suggests that this is approaching the lethal temperature fo r survival of A. nidulans.