The Tup1-Cyc8 Protein Complex Can Shift from a Transcriptional Co-repressor to a Transcriptional Co-activator*
- From the Institute of Molecular Biology and Biotechnology-Foundation of Research and Technology, Vassilika Vouton, P. O. Box 711 10 Heraklion, Crete, Greece
Abstract
Cyc8(Ssn6)-Tup1, a general co-repressor complex, is recruited to promoter DNA via interactions with DNA-binding regulatory proteins and inhibits the transcription of many different yeast genes. Previous studies have established that repression function of the complex is performed by one subunit of the complex, the Tup1 protein, and requires specific components of the RNA polymerase II holoenzyme such as Sin4 and Rgr1. In this study we test the transcriptional activity of the Cyc8 subunit using a lexAoperator-containing reporter. We show that a LexA-Cyc8 hybrid stimulates transcription when expressed in atup1Δ, a sin4Δ, or a rgr1Δstrain, suggesting that transcriptional activation is an intrinsic property of the Cyc8-Tup1 co-repressor. In support of this notion we demonstrate that Cyc8-Tup1 has a dual function on CIT2, a gene encoding a citrate synthase that is expressed upon mitochondrial dysfunction. First, we show that Cyc8-Tup1 is tethered toCIT2 promoter by interacting with the activation domain of Rtg3, a bHLH/L-Zip DNA-binding transactivator of CIT2. Next we demonstrate that Cyc8-Tup1 activates CIT2 transcription in response to mitochondrial dysfunction, and this stimulatory effect is mediated by Cyc8. In contrast, basal (noninduced) expression of this gene is inhibited by Tup1. These findings establish a positive role for the Cyc8-Tup1 complex in transcription and support a model by which specific metabolic signals may convert the Cyc8-Tup1 transcriptional co-repressor to a co-activator of certain promoters.
Footnotes
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↵* This work was supported by the Greek Ministry of Research and Technology (PENED) and by a Training and Mobility of Researchers grant from the European Union (to D. T.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed. Tel.: 81-391162; Fax: 81-391101; E-mail: Tzamarias{at}imbb.forth.gr.
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↵2 A. Ramne and P. S. Sunnerhagen, unpublished data.
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↵3 D. Tzamarias, unpublished observations.
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↵4 R. S. Conlan and D. Tzamarias, unpublished observations.
- Abbreviations:
- TPR
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tetratrico peptide repeat
- UAS
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X-Gal, 5-bromo-4-chloro-3-indolyl b-d-galactopyranoside
- GST
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glutathioneS-transferase
- PAGE
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polyacrylamide gel electrophoresis
- EMSA
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electrophoretic mobility shift assay
- bHLH
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basic helix-loop-helix
- UAS
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upstream activation sequence.
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- Received October 13, 1998.
- Revision received October 26, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
