Heat Shock Transcription Factor, X-Linked 1 (HSFX1)

Heat shock factors (HSF) are transcriptional activators of heat shock genes. They bind specifically to heat shock promoter elements, which are palindromic sequences rich with repetitive purine and pyrimidine motifs. Under normal conditions, HSF is a homo-trimeric cytoplasmic protein, but heat shock activation results in relocalisation to the nucleus.Each HSF monomer contains one C-terminal and three N-terminal leucine zipper repeats.Point mutations in these regions result in disruption of cellular localisation, rendering the protein constitutively nuclear. Two sequences flanking the N-terminal zippers fit the consensus of a bi-partite nuclear localization 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.