DNA-binding transcription factor that specifically binds heat shock promoter elements (HSE) and activates transcription. Homotrimer (PubMed:8175654). Homotrimerization increases the affinity of HSF1 to DNA (PubMed:8175654). Exhibits temperature-dependent phosphorylation that activates the transcriptional capacity. Inviable vegetative cell population. Belongs to the HSF family.