DNA-binding transcription factor that specifically binds heat shock promoter elements (HSE) and activates transcription (PubMed:27866167). Promotes thermotolerance by transiently regulating a subset of genes (PubMed:27866167). Induces expression of STI, SSA1, SSA2, HSP78 and KAR2 during the heat response (PubMed:27866167). Homotrimer (By similarity). Homotrimerization increases the affinity of HSF1 to DNA (By similarity). Interacts with transcriptional coregulator SSA1 on chromatin (By similarity). Repressed by high temperature (at protein level) (PubMed:27866167). Induced by oxidative stress (PubMed:27866167). Phosphorylated at high temperature. Inviable vegetative cell population (PubMed:27866167). Inviable spore (PubMed:27866167). Belongs to the HSF family.