Heat shock factor (HSF) is a transcriptional activator of heat shock genes[<cite idref="PUB00000842"/>]: it binds specifically to heat shock promoter elements, which arepalindromic sequences rich with repetitive purine and pyrimidine motifs [<cite idref="PUB00000842"/>].Under normal conditions, HSF is a homo-trimeric cytoplasmic protein, butheat shock activation results in relocalisation to the nucleus [<cite idref="PUB00004751"/>].Each HSF monomer contains one C-terminal and three N-terminal leucine zipperrepeats [<cite idref="PUB00006058"/>]. Point mutations in these regions result in disruption ofcellular localisation, rendering the protein constitutively nuclear [<cite idref="PUB00004751"/>].Two sequences flanking the N-terminal zippers fit the consensus of a bi-partite nuclear localisation signal (NLS). Interaction between the N- and C-terminal zippers may result in a structure that masks the NLS sequences: following activation of HSF, these may then be unmasked, resulting in relocalisation of the protein to the nucleus [<cite idref="PUB00006058"/>]. The DNA-binding componentof HSF lies to the N terminus of the first NLS region, and is referred toas the HSF domain. Heat shock factor (HSF)-type, DNA-binding