Function of the C-terminal transactivation domain of human heat shock factor 2 is modulated by the adjacent negative regulatory segment.

DNA binding of heat shock factor 2 (HSF2) is induced during hemin-induced differentiation of human erythroleukemia cell line K562. To identify the transcriptional activation and the regulatory domains of HSF2, we constructed a series of deletion derivatives fused to the yeast GAL4 DNA binding domain and analyzed their transactivation activity. A minimal transactivation domain of HSF2 was localized to the C-terminus (residues 472-536), as in HSF1, although amino acid sequence similarity for these regions was rather limited and the potential transactivation ability was about 25% that of HSF1. The transactivation mediated by this region of HSF2 was found to be negatively regulated by the adjacent 18 amino acid segment (residues 428-445) under normal conditions. Furthermore, the latter segment, when fused to the GAL4 activation domain, markedly inhibited GAL4 activity. Extract containing most derivatives of HSF2 retaining this segment exhibited doublet or triplet bands in gel mobility shift assays with heat shock element-containing DNA, suggesting possible involvement of some factors interacting with that segment in the negative regulation. Another putative transactivation domain and two negative regulatory regions were also localized within the internal region.