The Tup1-Cyc8 Protein Complex Can Shift from a Transcriptional Co-repressor to a Transcriptional Co-activator

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. 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. tetratrico peptide repeat X-Gal, 5-bromo-4-chloro-3-indolyl b-d-galactopyranoside glutathioneS-transferase polyacrylamide gel electrophoresis electrophoretic mobility shift assay basic helix-loop-helix upstream activation sequence. An important class of pleiotropic transcriptional regulators includes intermediary proteins such as co-activators and co-repressors. These protein factors are tethered to specific promoters mainly by contacting DNA-binding factors and regulate transcription either by interacting with components of the Pol II holoenzyme or by modifying chromatin structure, or both (1Kingston R.E. Bunker C.A. Imbalzano A.N. Genes Dev. 1996; 10: 905-920Crossref PubMed Scopus (403) Google Scholar, 2Shibata H. Spencer T.E. Onate S.A. Jenster G. Tsai S.Y. Tsai M.J. O'Malley B.W. Recent Prog. Horm. Res. 1997; 52: 141-164PubMed Google Scholar). The human co-activator CBP/p300 (3Korzus E. Torchia J. Rose D.W. Xu L. Kurokawa R. McInerney E.M. Mullen T.M. Glass C.K. Rosenfeld M.G. Science. 1998; 279: 703-707Crossref PubMed Scopus (558) Google Scholar), the yeast SAGA complex (4Roberts S.M. Winston F. Genetics. 1997; 2: 451-465Crossref Google Scholar), and the human nuclear receptor co-repressors SMRT and N-CoR (5Chen J.D. Evans R.M. Nature. 1995; 377: 454-457Crossref PubMed Scopus (1699) Google Scholar) are among the best characterized examples of this growing protein family. Interestingly, some of these factors have dual function on specific promoters; for example CBP/p300, which mediates activation of interferon β gene expression in response to virus induction is also responsible for post-induction turn off (35Munshi N. Merika M. Yie J. Senger K. Chen G. Thanos D. Mol. Cell. 1998; 2: 457-467Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar).In the yeast Saccharomyces cerevisiae, two physically associated proteins, Cyc8(Ssn6) and Tup1, inhibit the transcription of many diversely regulated genes when their expression is not required (6Williams F.E. Varanasi U. Trumbly R.J. Mol. Cell. Biol. 1991; 11: 3307-3331Crossref PubMed Scopus (174) Google Scholar, 7Keleher C.A. Redd M.J. Schultz J. Carlson M. Johnson A.D. Cell. 1992; 68: 709-719Abstract Full Text PDF PubMed Scopus (540) Google Scholar, 8Tzamarias D. Struhl K. Nature. 1994; 369: 758-761Crossref PubMed Scopus (281) Google Scholar). It is well established that Cyc8-Tup1 acts as a co-repressor complex that does not bind DNA directly but is recruited to different promoters via interactions with specific DNA-binding regulatory proteins. The repression function of the complex is performed by a specific domain of Tup1 (8Tzamarias D. Struhl K. Nature. 1994; 369: 758-761Crossref PubMed Scopus (281) Google Scholar). When the Tup1 repression domain is brought upstream of an active test promoter through the DNA binding domain of LexA, it inhibits transcription independently of Cyc8. Moreover, this domain is required for repression of natural genes such as glucose, oxygen, and cell-type regulated genes. It has been postulated that multiple mechanisms are responsible for Tup1 repression. Tup1 interacts with histones H3 and H4 and may position nucleosomes over the transcription start point, suggesting that Tup1 might repress transcription by modifying chromatin structure (9Roth S.Y. Curr. Opin. Genet. Dev. 1995; 5: 168-173Crossref PubMed Scopus (87) Google Scholar, 10Edmondson D.G. Smith M.M. Roth S.Y. Genes Dev. 1996; 10: 1247-1259Crossref PubMed Scopus (405) Google Scholar). However, evidence from other studies that Tup1 inhibits the function of the basic transcription Tup1 repression in an in transcription in the of chromatin Johnson Nature. 1994; PubMed Scopus Google Scholar), and in specific components of the RNA polymerase II holoenzyme complex, such as the proteins and the Tup1 repression activity F. Mol. Cell. Biol. 10: PubMed Scopus Google Scholar, U. 1995; PubMed Scopus Google Scholar, M. Johnson A.D. Genetics. 1995; PubMed Google Scholar, Carlson M. Mol. Cell. Biol. 1998; PubMed Scopus Google studies that Cyc8 does not directly inhibit transcription but specific DNA-binding regulatory proteins (8Tzamarias D. Struhl K. Nature. 1994; 369: 758-761Crossref PubMed Scopus (281) Google D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar). The of Cyc8 of of a tetratrico peptide repeat J. L. Carlson M. Mol. Cell. Biol. 10: PubMed Scopus Google Scholar). as and in the of are in structure Redd M.J. Johnson A.D. Genes Dev. 1995; PubMed Scopus Google Scholar, D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar, 1995; Full Text PDF PubMed Scopus Google Scholar, D. J. 1998; PubMed Scopus Google Scholar). and Tup1, different of to of Cyc8-Tup1 to different promoters D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar). on these it that the function of Cyc8 is to Tup1 to proteins. with this of Cyc8 that the domain are for repression. the other the domain which of the protein to J. L. Carlson M. Mol. Cell. Biol. 10: PubMed Scopus Google Scholar, Redd M.J. Johnson A.D. Genes Dev. 1995; PubMed Scopus Google Scholar, D. Struhl K. Genes Dev. 1995; PubMed Scopus Google that Cyc8-Tup1 might also a positive role in transcriptional activation of gene transcription by the transactivator and induction of gene both Cyc8 protein L. L. Genetics. 1994; PubMed Google Scholar, Carlson M. M. 1997; PubMed Scopus Google Scholar). In this we evidence that Cyc8-Tup1 in transcriptional of Cyc8-Tup1 genes is in response to specific and these the of the Cyc8-Tup1 co-repressor has been for of the that this complex convert to a co-activator of CIT2, a gene encoding a of citrate synthase that is expressed upon of mitochondrial Mol. Cell. Biol. 10: PubMed Scopus Google Scholar). We show that Cyc8-Tup1 is tethered to the CIT2 promoter by interacting with Rtg3, a DNA-binding transactivator of CIT2. that basal expression is inhibited by Tup1, but transcriptional activation is mediated by the of the complex, the Cyc8 subunit and requires the domain of this transcriptional activity of Cyc8 using a promoter and a LexA-Cyc8 Previous studies have that LexA-Cyc8 transcription by the Tup1 D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar). we show that LexA-Cyc8 transcription when Tup1 is or when the Tup1 repression is as it is in a or these an of the Cyc8-Tup1 co-repressor for transcriptional activation function and establish a dual role and of this complex in transcriptional this study we evidence for a dual role of Cyc8-Tup1 in transcriptional We that the well established repression which is performed by Tup1, the Cyc8-Tup1 protein complex also as a transcriptional and this function is mediated by the Cyc8 When the Tup1 repression activity is as it is in or a Cyc8-Tup1 activates an and in response to specific metabolic activates the transcription of the natural of CIT2 is by and both of the of DNA-binding proteins. and bind as a two an upstream activation of the CIT2 gene J. Biol. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, 1995; PubMed Scopus Google Scholar). promoters a to mitochondrial in a that is to Mol. Cell. Biol. 1991; 11: PubMed Scopus Google Scholar). using yeast of and that yeast proteins, co-activators or with the J. Mol. Cell. Biol. 1997; PubMed Scopus Google Scholar). show that Cyc8 and Tup1 are components of this protein The Cyc8-Tup1 complex with in and in and a DNA two to a complex, the of which is on the of the Cyc8 is mediated by two specific of to and to to with Tup1 D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar, Genetics. 1998; Google Scholar) different proteins and on these we that of Cyc8-Tup1 to promoter is mediated by specific that are responsible for of Cyc8 to Tup1 and of that complex to the of evidence that Cyc8-Tup1 is directly in the activation of CIT2 transcription and that this function is performed by the Cyc8 First, Cyc8-Tup1 with the activation domain of of has been to the activation domain of the which does not to to binding J. Biol. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). a role of the activation domain is to the Cyc8-Tup1 or of both and not the of of mitochondrial dysfunction. these CIT2 transcription is in the of Cyc8 and that and D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar). These that CIT2 transcription is not an effect of the In to of which pleiotropic as does not the when brought to a LexA-Cyc8 activates transcription in a the protein complex activates transcription in an or a that the for Tup1 repression. These with L. L. Genetics. 1994; PubMed Google Scholar, Carlson M. M. 1997; PubMed Scopus Google Scholar), establish a positive role of Cyc8 in transcription and a positive and function of the Cyc8-Tup1 protein complex on CIT2. Cyc8-Tup1 inhibits the basal expression and this function is performed by transcription is in in that Tup1, but Sin4 or CIT2 that Cyc8 activation function is performed in the of the Cyc8-Tup1 protein that CIT2 transcription requires the domain of and in this is the that a function has been to this When upstream of a test promoter through a DNA-binding domain this of Cyc8 does not transcription not it does not function as a activation but a regulatory Cyc8 is a and specific this in and are J. L. Carlson M. Mol. Cell. Biol. 10: PubMed Scopus Google Scholar). a which might also a regulatory role J. Biol. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). it is that specific of these protein such as or may in the transcriptional activity of of these in the domain of are to specific for the response of CIT2 as this domain is for the of other Cyc8-Tup1 that induction of genes upon mitochondrial are and using the the by which Cyc8-Tup1 is from a co-repressor to a co-activator of CIT2 is not model upon Tup1 from the complex Cyc8 activation However, performed with protein from either or on Mol. Cell. Biol. 10: PubMed Scopus Google J. Mol. Cell. Biol. 1997; PubMed Scopus Google Scholar). and D. also the model to which positive regulatory factors with Cyc8-Tup1 an complex, interactions with such factors model that in response to specific Cyc8-Tup1 which the intrinsic activation of Cyc8. of Tup1 for the activation function of the complex CIT2 induction is in the of Tup1 mechanisms by which proteins and transcription have been and in some as that of the these mechanisms have been characterized Kurokawa R. E.M. Rose D.W. Rosenfeld M.G. Glass C.K. Nature. 1998; PubMed Scopus Google Scholar). It is that Cyc8 specific by of the which is required for of CIT2 and this the through which the complex activation It that to this model of Cyc8 and of Tup1 have such an effect when the complex is associated with the proteins. Cyc8-Tup1 has a dual function in CIT2 expression and is not to an of a of mitochondrial not it is that Cyc8-Tup1 interacts with the basic transcription as well as with chromatin Carlson M. Mol. Cell. Biol. 1998; PubMed Scopus Google it is that Cyc8 might CIT2 transcription by either one or both An important class of pleiotropic transcriptional regulators includes intermediary proteins such as co-activators and co-repressors. These protein factors are tethered to specific promoters mainly by contacting DNA-binding factors and regulate transcription either by interacting with components of the Pol II holoenzyme or by modifying chromatin structure, or both (1Kingston R.E. Bunker C.A. Imbalzano A.N. Genes Dev. 1996; 10: 905-920Crossref PubMed Scopus (403) Google Scholar, 2Shibata H. Spencer T.E. Onate S.A. Jenster G. Tsai S.Y. Tsai M.J. O'Malley B.W. Recent Prog. Horm. Res. 1997; 52: 141-164PubMed Google Scholar). The human co-activator CBP/p300 (3Korzus E. Torchia J. Rose D.W. Xu L. Kurokawa R. McInerney E.M. Mullen T.M. Glass C.K. Rosenfeld M.G. Science. 1998; 279: 703-707Crossref PubMed Scopus (558) Google Scholar), the yeast SAGA complex (4Roberts S.M. Winston F. Genetics. 1997; 2: 451-465Crossref Google Scholar), and the human nuclear receptor co-repressors SMRT and N-CoR (5Chen J.D. Evans R.M. Nature. 1995; 377: 454-457Crossref PubMed Scopus (1699) Google Scholar) are among the best characterized examples of this growing protein family. Interestingly, some of these factors have dual function on specific promoters; for example CBP/p300, which mediates activation of interferon β gene expression in response to virus induction is also responsible for post-induction turn off (35Munshi N. Merika M. Yie J. Senger K. Chen G. Thanos D. Mol. Cell. 1998; 2: 457-467Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar). In the yeast Saccharomyces cerevisiae, two physically associated proteins, Cyc8(Ssn6) and Tup1, inhibit the transcription of many diversely regulated genes when their expression is not required (6Williams F.E. Varanasi U. Trumbly R.J. Mol. Cell. Biol. 1991; 11: 3307-3331Crossref PubMed Scopus (174) Google Scholar, 7Keleher C.A. Redd M.J. Schultz J. Carlson M. Johnson A.D. Cell. 1992; 68: 709-719Abstract Full Text PDF PubMed Scopus (540) Google Scholar, 8Tzamarias D. Struhl K. Nature. 1994; 369: 758-761Crossref PubMed Scopus (281) Google Scholar). It is well established that Cyc8-Tup1 acts as a co-repressor complex that does not bind DNA directly but is recruited to different promoters via interactions with specific DNA-binding regulatory proteins. The repression function of the complex is performed by a specific domain of Tup1 (8Tzamarias D. Struhl K. Nature. 1994; 369: 758-761Crossref PubMed Scopus (281) Google Scholar). When the Tup1 repression domain is brought upstream of an active test promoter through the DNA binding domain of LexA, it inhibits transcription independently of Cyc8. Moreover, this domain is required for repression of natural genes such as glucose, oxygen, and cell-type regulated genes. It has been postulated that multiple mechanisms are responsible for Tup1 repression. Tup1 interacts with histones H3 and H4 and may position nucleosomes over the transcription start point, suggesting that Tup1 might repress transcription by modifying chromatin structure (9Roth S.Y. Curr. Opin. Genet. Dev. 1995; 5: 168-173Crossref PubMed Scopus (87) Google Scholar, 10Edmondson D.G. Smith M.M. Roth S.Y. Genes Dev. 1996; 10: 1247-1259Crossref PubMed Scopus (405) Google Scholar). However, evidence from other studies that Tup1 inhibits the function of the basic transcription Tup1 repression in an in transcription in the of chromatin Johnson Nature. 1994; PubMed Scopus Google Scholar), and in specific components of the RNA polymerase II holoenzyme complex, such as the proteins and the Tup1 repression activity F. Mol. Cell. Biol. 10: PubMed Scopus Google Scholar, U. 1995; PubMed Scopus Google Scholar, M. Johnson A.D. Genetics. 1995; PubMed Google Scholar, Carlson M. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). Previous studies that Cyc8 does not directly inhibit transcription but specific DNA-binding regulatory proteins (8Tzamarias D. Struhl K. Nature. 1994; 369: 758-761Crossref PubMed Scopus (281) Google D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar). The of Cyc8 of of a tetratrico peptide repeat J. L. Carlson M. Mol. Cell. Biol. 10: PubMed Scopus Google Scholar). as and in the of are in structure Redd M.J. Johnson A.D. Genes Dev. 1995; PubMed Scopus Google Scholar, D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar, 1995; Full Text PDF PubMed Scopus Google Scholar, D. J. 1998; PubMed Scopus Google Scholar). and Tup1, different of to of Cyc8-Tup1 to different promoters D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar). on these it that the function of Cyc8 is to Tup1 to proteins. with this of Cyc8 that the domain are for repression. the other the domain which of the protein to J. L. Carlson M. Mol. Cell. Biol. 10: PubMed Scopus Google Scholar, Redd M.J. Johnson A.D. Genes Dev. 1995; PubMed Scopus Google Scholar, D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar). Recent that Cyc8-Tup1 might also a positive role in transcriptional activation of gene transcription by the transactivator and induction of gene both Cyc8 protein L. L. Genetics. 1994; PubMed Google Scholar, Carlson M. M. 1997; PubMed Scopus Google Scholar). In this we evidence that Cyc8-Tup1 in transcriptional of Cyc8-Tup1 genes is in response to specific and these the of the Cyc8-Tup1 co-repressor has been for of the that this complex convert to a co-activator of CIT2, a gene encoding a of citrate synthase that is expressed upon of mitochondrial Mol. Cell. Biol. 10: PubMed Scopus Google Scholar). We show that Cyc8-Tup1 is tethered to the CIT2 promoter by interacting with Rtg3, a DNA-binding transactivator of CIT2. that basal expression is inhibited by Tup1, but transcriptional activation is mediated by the of the complex, the Cyc8 subunit and requires the domain of this The transcriptional activity of Cyc8 using a promoter and a LexA-Cyc8 Previous studies have that LexA-Cyc8 transcription by the Tup1 D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar). we show that LexA-Cyc8 transcription when Tup1 is or when the Tup1 repression is as it is in a or these an of the Cyc8-Tup1 co-repressor for transcriptional activation function and establish a dual role and of this complex in transcriptional this study we evidence for a dual role of Cyc8-Tup1 in transcriptional We that the well established repression which is performed by Tup1, the Cyc8-Tup1 protein complex also as a transcriptional and this function is mediated by the Cyc8 When the Tup1 repression activity is as it is in or a Cyc8-Tup1 activates an and in response to specific metabolic activates the transcription of the natural of CIT2 is by and both of the of DNA-binding proteins. and bind as a two an upstream activation of the CIT2 gene J. Biol. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, 1995; PubMed Scopus Google Scholar). promoters a to mitochondrial in a that is to Mol. Cell. Biol. 1991; 11: PubMed Scopus Google Scholar). using yeast of and that yeast proteins, co-activators or with the J. Mol. Cell. Biol. 1997; PubMed Scopus Google Scholar). show that Cyc8 and Tup1 are components of this protein The Cyc8-Tup1 complex with in and in and a DNA two to a complex, the of which is on the of the Cyc8 is mediated by two specific of to and to to with Tup1 D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar, Genetics. 1998; Google Scholar) different proteins and on these we that of Cyc8-Tup1 to promoter is mediated by specific that are responsible for of Cyc8 to Tup1 and of that complex to the of evidence that Cyc8-Tup1 is directly in the activation of CIT2 transcription and that this function is performed by the Cyc8 First, Cyc8-Tup1 with the activation domain of of has been to the activation domain of the which does not to to binding J. Biol. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). a role of the activation domain is to the Cyc8-Tup1 or of both and not the of of mitochondrial dysfunction. these CIT2 transcription is in the of Cyc8 and that and D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar). These that CIT2 transcription is not an effect of the In to of which pleiotropic as does not the when brought to a LexA-Cyc8 activates transcription in a the protein complex activates transcription in an or a that the for Tup1 repression. These with L. L. Genetics. 1994; PubMed Google Scholar, Carlson M. M. 1997; PubMed Scopus Google Scholar), establish a positive role of Cyc8 in transcription and a positive and function of the Cyc8-Tup1 protein complex on CIT2. Cyc8-Tup1 inhibits the basal expression and this function is performed by transcription is in in that Tup1, but Sin4 or CIT2 that Cyc8 activation function is performed in the of the Cyc8-Tup1 protein that CIT2 transcription requires the domain of and in this is the that a function has been to this When upstream of a test promoter through a DNA-binding domain this of Cyc8 does not transcription not it does not function as a activation but a regulatory Cyc8 is a and specific this in and are J. L. Carlson M. Mol. Cell. Biol. 10: PubMed Scopus Google Scholar). a which might also a regulatory role J. Biol. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). it is that specific of these protein such as or may in the transcriptional activity of of these in the domain of are to specific for the response of CIT2 as this domain is for the of other Cyc8-Tup1 that induction of genes upon mitochondrial are and using the the by which Cyc8-Tup1 is from a co-repressor to a co-activator of CIT2 is not model upon Tup1 from the complex Cyc8 activation However, performed with protein from either or on Mol. Cell. Biol. 10: PubMed Scopus Google J. Mol. Cell. Biol. 1997; PubMed Scopus Google Scholar). and D. also the model to which positive regulatory factors with Cyc8-Tup1 an complex, interactions with such factors model that in response to specific Cyc8-Tup1 which the intrinsic activation of Cyc8. of Tup1 for the activation function of the complex CIT2 induction is in the of Tup1 mechanisms by which proteins and transcription have been and in some as that of the these mechanisms have been characterized Kurokawa R. E.M. Rose D.W. Rosenfeld M.G. Glass C.K. Nature. 1998; PubMed Scopus Google Scholar). It is that Cyc8 specific by of the which is required for of CIT2 and this the through which the complex activation It that to this model of Cyc8 and of Tup1 have such an effect when the complex is associated with the proteins. Cyc8-Tup1 has a dual function in CIT2 expression and is not to an of a of mitochondrial not it is that Cyc8-Tup1 interacts with the basic transcription as well as with chromatin Carlson M. Mol. Cell. Biol. 1998; PubMed Scopus Google it is that Cyc8 might CIT2 transcription by either one or both In this study we evidence for a dual role of Cyc8-Tup1 in transcriptional We that the well established repression which is performed by Tup1, the Cyc8-Tup1 protein complex also as a transcriptional and this function is mediated by the Cyc8 When the Tup1 repression activity is as it is in or a Cyc8-Tup1 activates an and in response to specific metabolic activates the transcription of the natural of CIT2 is by and both of the of DNA-binding proteins. and bind as a two an upstream activation of the CIT2 gene J. Biol. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar, 1995; PubMed Scopus Google Scholar). promoters a to mitochondrial in a that is to Mol. Cell. Biol. 1991; 11: PubMed Scopus Google Scholar). using yeast of and that yeast proteins, co-activators or with the J. Mol. Cell. Biol. 1997; PubMed Scopus Google Scholar). show that Cyc8 and Tup1 are components of this protein The Cyc8-Tup1 complex with in and in and a DNA two to a complex, the of which is on the of the Cyc8 is mediated by two specific of to and to to with Tup1 D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar, Genetics. 1998; Google Scholar) different proteins and on these we that of Cyc8-Tup1 to promoter is mediated by specific that are responsible for of Cyc8 to Tup1 and of that complex to the of evidence that Cyc8-Tup1 is directly in the activation of CIT2 transcription and that this function is performed by the Cyc8 First, Cyc8-Tup1 with the activation domain of of has been to the activation domain of the which does not to to binding J. Biol. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). a role of the activation domain is to the Cyc8-Tup1 or of both and not the of of mitochondrial dysfunction. these CIT2 transcription is in the of Cyc8 and that and D. Struhl K. Genes Dev. 1995; PubMed Scopus Google Scholar). These that CIT2 transcription is not an effect of the In to of which pleiotropic as does not the when brought to a LexA-Cyc8 activates transcription in a the protein complex activates transcription in an or a that the for Tup1 repression. These with L. L. Genetics. 1994; PubMed Google Scholar, Carlson M. M. 1997; PubMed Scopus Google Scholar), establish a positive role of Cyc8 in transcription and a positive and function of the Cyc8-Tup1 protein complex on CIT2. Cyc8-Tup1 inhibits the basal expression and this function is performed by transcription is in in that Tup1, but Sin4 or CIT2 that Cyc8 activation function is performed in the of the Cyc8-Tup1 protein that CIT2 transcription requires the domain of and in this is the that a function has been to this When upstream of a test promoter through a DNA-binding domain this of Cyc8 does not transcription not it does not function as a activation but a regulatory Cyc8 is a and specific this in and are J. L. Carlson M. Mol. Cell. Biol. 10: PubMed Scopus Google Scholar). a which might also a regulatory role J. Biol. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). it is that specific of these protein such as or may in the transcriptional activity of of these in the domain of are to specific for the response of CIT2 as this domain is for the of other Cyc8-Tup1 genes. The that induction of genes upon mitochondrial are and using the the by which Cyc8-Tup1 is from a co-repressor to a co-activator of CIT2 is not model upon Tup1 from the complex Cyc8 activation However, performed with protein from either or on Mol. Cell. Biol. 10: PubMed Scopus Google J. Mol. Cell. Biol. 1997; PubMed Scopus Google Scholar). and D. also the model to which positive regulatory factors with Cyc8-Tup1 an complex, interactions with such factors model that in response to specific Cyc8-Tup1 which the intrinsic activation of Cyc8. of Tup1 for the activation function of the complex CIT2 induction is in the of Tup1 mechanisms by which proteins and transcription have been and in some as that of the these mechanisms have been characterized Kurokawa R. E.M. Rose D.W. Rosenfeld M.G. Glass C.K. Nature. 1998; PubMed Scopus Google Scholar). It is that Cyc8 specific by of the which is required for of CIT2 and this the through which the complex activation It that to this model of Cyc8 and of Tup1 have such an effect when the complex is associated with the proteins. Cyc8-Tup1 has a dual function in CIT2 expression and is not to an of a of mitochondrial not it is that Cyc8-Tup1 interacts with the basic transcription as well as with chromatin Carlson M. Mol. Cell. Biol. 1998; PubMed Scopus Google it is that Cyc8 might CIT2 transcription by either one or both We and for D. for the and for RNA