Structural organization and promoter analysis of murine heat shock transcription factor-1 gene

Heat shock factor-1 (HSF-1) activates transcription of heat shock proteins in eukaryotes. Several overlapping genomic clones containing the murine HSF -1 gene were isolated from a phage genomic library. Results indicate that t he HSF-1 gene contains 13 exons that span at least 30 kilobase pairs. Seque nce analysis of the 5'-untranslated region of HSF-1 suggests that it contai ns sequences of a recently described Bop1 gene in reverse orientation withi n its first 331 base pairs (bp) upstream of the translation initiation site . The minimal promoter sequence required for HSF-1 basal expression was ide ntified by deletion analysis from -4 kilobase pairs to -331 bp of the promo ter fused to a luciferase reporter gene using transient transfection assays . Results indicate that 331 bp upstream of the HSF-1 translation start site is required for maximal basal expression in NIH3T3 and F9 cells. This frag ment also results in high levels of luciferase activity in the reverse orie ntation, that is, 5' to the Bop1 gene, suggesting that this segment is bidi rectional and could be utilized for basal expression of both HSF-1 and Bop1 genes. This segment of the promoter contains recognition elements for Spl and CCAAT-box binding transcription factors, which when mutated in either s ense or antisense orientations to the HSF-1 gene results in a reduction of basal expression by 50-75% relative to mild type, suggesting that these sit es are critical for basal expression of both HSF-1 and Bop1 genes.