Transcriptional activator that specifically binds DNA sequence 5'-AGAAnnTTCT-3' known as heat shock promoter elements (HSE). Homotrimer (By similarity). Binds to HSBP (PubMed:20388662, PubMed:20657173). DNA-binding capacity is reduced by HSBP in vitro. The hydrophobic-rich region (HR-A/B) corresponds to the oligomerization domain. AHA motif is a transcriptional activator element. Exhibits temperature-dependent phosphorylation. Belongs to the HSF family. Class A subfamily. Truncated N-terminus.