Heat-shock transcription factor that specifically binds heat shock promoter elements (HSE) (By similarity). Required for denucleation and organelle rupture and degradation that occur during eye lens terminal differentiation, when fiber cells that compose the lens degrade all membrane-bound organelles in order to provide lens with transparency to allow the passage of light (By similarity). In this process, may regulate denucleation of lens fiber cells in part by activating DNASE2B transcription (By similarity). May be involved in DNA repair through the transcriptional regulation of RAD51 (By similarity). May up-regulate p53/TP53 protein in eye lens fiber cells, possibly through protein stabilization (By similarity). In the eye lens, controls the expression of alpha-crystallin B chain/CRYAB and consequently may be involved in the regulation of lysosomal acidification (By similarity). Homotrimer. Exhibits constitutive DNA binding and forms trimers even in the absence of stress. Interacts with ALKBH4, DUSP26, MAPK1, MAPK2, MAPK8 and MAP kinase p38. Phosphorylated mainly on serine residues. Phosphorylation on Ser-299 promotes sumoylation on Lys-294 (By similarity). Constitutively sumoylated. Sumoylation represses the transcriptional activity and is promoted by phosphorylation on Ser-299 (By similarity). Defects in HSF4 are a cause of forms of hereditary cataract (HC) in dogs. Mutations in HSF4 seem to be causing a recessive form of cataract in Staffordshire Bull terriers and Boston terriers and a dominant cataract in Australian shepherds. Belongs to the HSF family.