Fig. 5. HSF1 is the major component of the heat-induced HSE-binding complex. (A) Cells were subjected to different periods of heat shock (HS; 1-6 h) or left untreated (C). The HSF DNA-binding activity in the whole cell extracts was analyzed by gel mobility shift assay with radiolabeled HSE (left panel). Antibody perturbations with Flag and Myc antibodies (1:10) were used to detect the presence of HSF1 or HSF2 in the DNA-binding complex, respectively (right panel). A hemin-treated sample was used as a control. An empty Myc vector was used in the mock transfections. (B) Flag antibodies were used to immunoprecipitate HSF1 from the same lysates as in panel A. Western blotting was performed as in Fig. 3. The expression levels are presented in the right hand panel (WB). Arrows and asterisks indicate the inducibly phosphorylated HSF1 and the endogenous HSF2, respectively.

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