Constitutive and heat inducible heat shock element binding activities of heat shock factor in a group of filamentous fungi

This study represents the initial characterization of the heat shock factor (HSF) in filamentous fungi. We demonstrate that HSFs from Beauveria bassia na, Metarhizium anisopliae, Tolypocladium nivea, Paecilomyces farinosus, an d Verticillium lecanii bind to the heat shock element (HSE) constitutively (non-shocked), and that heat shock resulted in increased quantities and dec reased mobility of HSF-HSE complexes. The monomeric molecular mass of both heat-induced and constitutive HSFs was determined to be 85.8 kDa by UV-cros slinking and the apparent molecular masses of the native HSF-HSE complexes as determined by pore exclusion gradient gel electrophoresis was 260 and 30 0 kDa, respectively. Proteolytic band clipping assays using trypsin and chy motrypsin revealed an identical partial cleavage profile for constitutive a nd heat-induced HSF-HSE complexes. Thus, it appears that both constitutive and heat-inducible complexes are formed by trimers composed of the same HSF molecule which undergoes conformational changes during heat shock. The mob ility difference between the complexes was not abolished by enzymatic depho sphorylation and deglycosylation, indicating that the reduced mobility of t he heat-induced HSF is probably due to a post-translational modification ot her than phosphorylation or glycosylation. (C) 1999 Harcourt Publishers Ltd .