DNA-binding protein that specifically binds heat shock promoter elements (HSE) and activates transcription. In higher eukaryotes, HSF is unable to bind to the HSE unless the cells are heat shocked. HSF2 is expressed in a form that binds DNA constitutively but loses DNA binding by incubation at greater than 41 degrees C. DNA-binding homotrimer in stressed or heat shocked cells, otherwise found as a homodimer. Cytoplasmic during normal growth and moves to the nucleus upon activation. Isoform alpha is expressed predominantly in testis while isoform beta is expressed predominantly in heart and brain. In the 7-day-old testis, isoform beta is expressed at significantly higher levels than isoform alpha. As development proceeds, the levels of isoform alpha gradually increase so that it is the predominant isoform in mature testes. Belongs to the HSF family.