Multiple responses to heat stress by the basidiomyceteSchizophyllum commune

Temperatures in excess of 45°C are required to stop the growth ofSchizophyllum commune colonies. Transfer of colonies from normal growth conditions (21°C) to 55°C, while halting mycelial expansion and increasing the production of aerial hyphae, was not lethal. Shortterm heat shock (3h) resulted in the appearance of nine proteins resolvable by SDS-PAGE that were newly synthesized or had their synthesis increased. The molecular weights of these proteins qualify two of them as being members of the hsp90 and hsp 70 families of heat shock proteins. Heat shock also affected proteolytic processes in the colonies. Changes in the pattern of ubiquitinated protein conjugates occurred; fewer high-molecular-weight conjugates were found in heat-shocked colonies, and the appearance of a ladder of lower-molecular-weight conjugates was noted. Protease enzymes detected by gelatin-gel PAGE showed a general decrease in activity. One of these proteases, which was up-regulated during nitrogen deprivation, showed an intermediate response during the combined stresses of heat shock and nitrogen starvation.