The induction of heat-shock proteins has been postulated to play a role not only in thermo-adaptation, but also in phase transition of the dimorphic fungi. In this study, we used yeast and mycelial forms of the thermally dimorphic fungus to evaluate the effect of temperature on the induction of the heat-shock response. We also evaluated protein synthesis by caused by exposure to low pH and HO. Analysis of protein synthesis by SDS-PAGE disclosed that mycelia increased synthesis of all major constitutive proteins when stressed at 37°C and increased synthesis of three non-constitutive proteins of 134, 82 and 28 kDa at 40°C. Yeasts incubated at 40°C showed decreased synthesis of five constitutive proteins (136, 98, 62, 57 and 54 kDa) and the appearance of three new proteins (134, 82 and 28 kDa). There was a decrease in the synthesis of all major constitutive proteins except for three proteins of 141, 136 and 16 kDa when yeast cells were incubated at 25°C. When stressed by low pH and HO, yeast increased synthesis of one (134 kDa) and five (134, 104, 82, 52 and 40 kDa) non-constitutive proteins, respectively. mycelia and yeast forms disclosed the same profile of protein synthesis when stressed at temperatures that trigger phase transition (37°C for mycelia; 25°C for yeast). The same profile of protein synthesis by both forms occurred when the fungi were incubated at 40°C and was similar to that of yeast cells stressed by low pH or HO, but different from the patterns produced by mycelia incubated at 37°C or yeast at 25°C. These results suggest that synthesis of stress proteins by mycelia and yeast forms at 40°C, low pH or exposed to HO was associated with adaptation to hostile environments. In contrast, the overall increased and decreased synthesis of major constitutive proteins by mycelia and yeast forms at 37°C and 25°C was associated with phase transition. It is unlikely that the heat-shock proteins produced in these experiments are important in the maintenance of the morphology of yeast or mycelia at their usual temperatures of growth.


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