DNA-binding transcription factor that specifically binds heat shock promoter elements (HSE) and activates transcription. With HSP90, is required for the modulation of the chaperone levels in response to growth temperature, rather than the activation of acute responses to sudden thermal transitions. Activated during infection and contributes to full virulence. Homotrimer (By similarity). Homotrimerization increases the affinity of HSF1 to DNA (By similarity). Interacts with HSP90 (PubMed:23300438). Induced during exposure to the weak acid stress of acetic acid, through the regulation by the transcription factor MNL1. Activated by phosphorylation of at least Ser-570, Thr-574, Ser-576 and Thr-577 in response to heat shock. Additional unidentified residues are also phosphorylated in response to heat shock. Leads to lethality. Belongs to the HSF family.