Heat shock factor-4 (HSF-4a) represses basal transcription through interaction with TFIIF.
The heat shock transcription factors (HSFs) regulate the expression of heat shock proteins (hsps), which are critical for normal cellular proliferation and differentiation. One of the HSFs, HSF-4, contains two alternative splice variants, one of which possesses transcriptional repressor properties in vivo. This repressor isoform inhibits basal transcription of hsps 27 and 90 in tissue culture cells. The molecular mechanisms of HSF-4a isoform-mediated transcriptional repression is unknown. Here, we present evidence that HSF-4a inhibits basal transcription in vivo when it is artificially targeted to basal promoters via the DNA-binding domain of the yeast transcription factor, GAL4. By using a highly purified, reconstituted in vitro transcription system, we show that HSF-4a represses basal transcription at an early step during preinitiation complex assembly, as pre-assembled preinitiation complexes are refractory to the inhibitory effect on transcription. This repression occurs by the HSF-4a isoform, but not by the HSF-4b isoform, which we show is capable of activating transcription from a heat shock element-driven promoter in vitro. The repression of basal transcription by HSF-4a occurs through interaction with the basal transcription factor TFIIF. TFIIF interacts with a segment of HSF-4a that is required for the trimerization of HSF-4a, and deletion of this segment no longer inhibits basal transcription. These studies suggest that HSF-4a inhibits basal transcription both in vivo and in vitro. Furthermore, this is the first report identifying an interaction between a transcriptional repressor with the basal transcription factor TFIIF.
Institute of Molecular Medicine and Genetics and Department of Radiology, Medical College of Georgia, Augusta, Georgia 30912, USA.
W
W
Frejtag
Y
Y
Zhang
R
R
Dai
M G
MG
Anderson
N F
NF
Mivechi
D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D000076249:Heat Shock Transcription Factors; D006801:Humans; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014157:Transcription Factors / Q000378:metabolism* / Q000502:physiology*; D019473:Transcription Factors, TFII; D014158:Transcription, Genetic / Q000502:physiology*
D004268:DNA-Binding Proteins; C102948:HSF4 protein, human; D000076249:Heat Shock Transcription Factors; D014157:Transcription Factors; D019473:Transcription Factors, TFII; C056604:transcription factor TFIIF