Nucleic Acids Research, 2001, Vol. 29, No. 8 1715-1723
© 2001 Oxford University Press
The wing in yeast heat shock transcription factor (HSF) DNA-binding domain is required for full activity
Johnson Research Foundation and Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6089, USA and 1Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3206, USA
The yeast heat shock transcription factor (HSF) belongs to the winged helix family of proteins. HSF binds DNA as a trimer, and additional trimers can bind DNA co-operatively. Unlike other winged helix–turn–helix proteins, HSF’s wing does not appear to contact DNA, as based on a previously solved crystal structure. Instead, the structure implies that the wing is involved in protein–protein interactions, possibly within a trimer or between adjacent trimers. To understand the function of the wing in the HSF DNA-binding domain, a Saccharomyces cerevisiae strain was created that expresses a wingless HSF protein. This strain grows normally at 30°C, but shows a decrease in reporter gene expression during constitutive and heat-shocked conditions. Removal of the wing does not affect the stability or trimeric nature of a protein fragment containing the DNA-binding and trimerization domains. Removal of the wing does result in a decrease in DNA-binding affinity. This defect was mainly observed in the ability to form the first trimer-bound complex, as the formation of larger complexes is unaffected by the deletion. Our results suggest that the wing is not involved in the highly co-operative nature of HSF binding, but may be important in stabilizing the first trimer bound to DNA.
* To whom correspondence should be addressed at: University of Pennsylvania School of Medicine, 813 Stellar-Chance #6089, Philadelphia, PA 19104-6089, USA. Tel: +1 215 573 7473; Fax: +1 215 573 2503; Email: hnelson{at}mail.med.upenn.edu
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