Transcriptional regulator that specifically binds DNA sequence 5'-AGAAnnTTCT-3' known as heat shock promoter elements (HSE). Homotrimer (By similarity). Interacts with HSP90-2 (PubMed:17965410). The hydrophobic-rich region (HR-A/B) corresponds to the oligomerization domain. Exhibits temperature-dependent phosphorylation. Belongs to the HSF family. Class A subfamily.