DNA-binding transcription factor that specifically binds heat shock promoter elements (HSE) and activates transcription (PubMed:17040492). Together with its coregulator SSA1, activates expression of laccase LAC1 during glucose starvation (PubMed:17040492). Homotrimer (By similarity). Homotrimerization increases the affinity of HSF1 to DNA (By similarity). Interacts with transcriptional coregulator SSA1 on chromatin (PubMed:17040492). Belongs to the HSF family.