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doi:10.1534/genetics.104.037143
A more recent version of this article appeared on March 1, 2005.
REGULAR RESEARCH PAPERS |
The Heme Activator Protein Hap1 Represses Transcription by a Heme-Independent Mechanism in Saccharomyces Cerevisiae
Thomas Hon 1, Hee Chul Lee 1, Zhanzhi Hu 2, Vishwanath R Iyer 2 and Li Zhang 1*
1 Columbia University
2 University of Texas at Austin
* To whom correspondence should be addressed. E-mail: lz2115{at}columbia.edu.
Submitted on October 6, 2004
Revised on November 15, 2004
Accepted on 30 November 2004
The yeast heme activator protein Hap1 binds to DNA and activates transcription of genes encoding functions required for respiration and for controlling oxidative damage, in response to heme. Hap1 contains a DNA-binding domain with a C6 zinc cluster motif and a coiled-coil dimerization element, typical of the members of the yeast Gal4 family, and an acidic activation domain. The regulation of Hap1 transcription-activating activity is controlled by two classes of Hap1 elements, repression modules (RPM1-3) and heme-responsive motifs (HRM1-7). Previous indirect evidence indicates that Hap1 may repress transcription directly. Here we show, by promoter analysis, by chromatin immunoprecipitation, and by electrophoretic mobility shift assay, that Hap1 binds directly to DNA and represses transcription of its own gene by at least 20-fold. We found that Hap1 repression of the HAP1 gene occurs independently of heme concentrations. While DNA binding is required for transcriptional repression by Hap1, deletion of Hap1 activation domain and heme-regulatory elements has varying effects on repression. Further, we found that repression by Hap1 requires the function of Hsp70 (Ssa), but not Hsp90. These results show that Hap1 binds to its own promoter and represses transcription in a heme-independent but Hsp70-dependent manner.
Key Words: Hap1, heme, promoter, repression, transcription
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