a transcription factor that specifically binds heat shock promoter elements (HSE) and activates transcription. Induced in response to heat, heavy metals, and oxidative stress. In higher eukaryotes, HSF is unable to bind to HSEs unless the cells are stressed. Becomes phosphorylated in response to stress, forming homotrimers that bind DNA and activate transcription. Phosphorylation by PLK1 enhances nuclear translocation, and phosphorylation by CaMKII enhances transactivation. Phosphorylation by GSK3 and ERK1 induces binding by 14-3-3 and sequestration in the cytoplasm. In addition, during attenuation from the heat shock response, HSF1 is repressed by direct binding of Hsp70, HSP40, and HSF binding protein 1 (HSBP1). Four alternatively spliced isoforms have been described. Note: This description may include information from UniProtKB.