YEAF1/RYBP and YAF-2 Are Functionally Distinct Members of a Cofactor Family for the YY1 and E4TF1/hGABP Transcription Factors

Abstract

The transcription factor hGABP/E4TF1 is a heterotetrameric complex composed of two DNA-binding subunits (hGABPα/E4TF1–60) and two transactivating subunits (hGABPβ/E4TF1–53). In order to understand the molecular mechanism of transcriptional regulation by hGABP, we searched for proteins that interact with the non-DNA-binding subunit, hGABPβ, using yeast two-hybrid screening. We identified a human cDNA encoding a protein related to YAF-2 (YY1-associated factor 2), which was previously isolated as an interacting partner of the Ying-Yang-1 (YY1) transcription factor. Reflecting this similarity, both YAF-2 and this novel protein (named YEAF1 for YY1- andE4TF1/hGABP-associatedfactor-1) interacted with hGABPβ and YY1in vitro and in vivo, indicating that YEAF1 and YAF-2 constitute a cofactor family for these two structurally distinct transcription factors. By using yeast three-hybrid assay, we demonstrated that hGABPβ and YY1 formed a complex only in the presence of YEAF1, indicating that YEAF1 is a bridging factor of these two transcription factors. These cofactors are functionally different in that YAF-2 positively regulates the transcriptional activity of hGABP but YEAF1 negatively regulates this activity. Also,YAF-2 mRNA is highly expressed in skeletal muscle, whereas YEAF1 mRNA is highly expressed in placenta. We speculate that the transcriptional activity of hGABP is in part regulated by the expression levels of these tissue-specific cofactors. These results provide a novel mechanism of transcriptional regulation by functionally distinct cofactor family members. The transcription factor hGABP/E4TF1 is a heterotetrameric complex composed of two DNA-binding subunits (hGABPα/E4TF1–60) and two transactivating subunits (hGABPβ/E4TF1–53). In order to understand the molecular mechanism of transcriptional regulation by hGABP, we searched for proteins that interact with the non-DNA-binding subunit, hGABPβ, using yeast two-hybrid screening. We identified a human cDNA encoding a protein related to YAF-2 (YY1-associated factor 2), which was previously isolated as an interacting partner of the Ying-Yang-1 (YY1) transcription factor. Reflecting this similarity, both YAF-2 and this novel protein (named YEAF1 for YY1- andE4TF1/hGABP-associatedfactor-1) interacted with hGABPβ and YY1in vitro and in vivo, indicating that YEAF1 and YAF-2 constitute a cofactor family for these two structurally distinct transcription factors. By using yeast three-hybrid assay, we demonstrated that hGABPβ and YY1 formed a complex only in the presence of YEAF1, indicating that YEAF1 is a bridging factor of these two transcription factors. These cofactors are functionally different in that YAF-2 positively regulates the transcriptional activity of hGABP but YEAF1 negatively regulates this activity. Also,YAF-2 mRNA is highly expressed in skeletal muscle, whereas YEAF1 mRNA is highly expressed in placenta. We speculate that the transcriptional activity of hGABP is in part regulated by the expression levels of these tissue-specific cofactors. These results provide a novel mechanism of transcriptional regulation by functionally distinct cofactor family members. adenovirus early 4 Ying-Yang-1 YY1-associated factor 2 human GA-binding protein YY1- and E4TF1/hGABP-associated factor-1 Ring1 and YY1 binding protein 3-aminotriazol Glutathione S-transferase retinoblastoma susceptibility gene conserved region, OR, original region surface plasmon resonance Polycomb group E4TF1 was originally purified from HeLa cells and was identified as one of the sequence-specific transcription factors that bind to and stimulate transcription from the adenovirus early 4 (E4)1 promoter (1Watanabe H. Imai T. Sharp P.A. Handa H. Mol. Cell. Biol. 1988; 8: 1290-1300Crossref PubMed Scopus (39) Google Scholar, 2Watanabe H. Wada T. Handa H. EMBO J. 1990; 9: 841-847Crossref PubMed Scopus (60) Google Scholar). Subsequent cDNA cloning and nucleotide sequence analyses (3Watanabe H. Sawada J.-i. Yano K. Yamaguchi K. Goto M. Handa H. Mol. Cell. Biol. 1993; 13: 1385-1391Crossref PubMed Scopus (91) Google Scholar, 4Sawada J.-i. Goto M. Sawa C. Watanabe H. Handa H. EMBO J. 1994; 13: 1396-1402Crossref PubMed Scopus (46) Google Scholar) have revealed that it is a human homologue of the rat GA-binding protein (hGABP), which binds to the GA motif of the herpes simplex virus immediate early genes and stimulates their transcription (5LaMarco K. Thompson C.C. Byers B.P. Walton E.M. McKnight S.L. Science. 1991; 253: 789-792Crossref PubMed Scopus (259) Google Scholar,6Thompson C.C. Brown T.A. McKnight S.L. Science. 1991; 253: 762-768Crossref PubMed Scopus (320) Google Scholar). E4TF1/hGABP is a unique transcription factor in its subunit composition. It is a heterotetramer (α2β2) of two 60-kDa (E4TF1–60/hGABPα) and two 53-kDa (E4TF1–53/hGABPβ) subunits. Structural and biochemical analyses (3Watanabe H. Sawada J.-i. Yano K. Yamaguchi K. Goto M. Handa H. Mol. Cell. Biol. 1993; 13: 1385-1391Crossref PubMed Scopus (91) Google Scholar, 4Sawada J.-i. Goto M. Sawa C. Watanabe H. Handa H. EMBO J. 1994; 13: 1396-1402Crossref PubMed Scopus (46) Google Scholar, 7Sawa C. Goto M. Suzuki F. Watanabe H. Sawada J.-i. Handa H. Nucleic Acids Res. 1996; 24: 4954-4961Crossref PubMed Scopus (47) Google Scholar, 8Suzuki F. Goto M. Sawa C. Ito S. Watanabe H. Sawada J.-i. Handa H. J. Biol. Chem. 1998; 273: 29302-29308Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar) have revealed that hGABPα contains an Ets-related DNA-binding domain and can bind to the DNA sequence 5′-CGGAAGTG-3′. However, hGABPα alone is unable to activate transcription, and the transactivator function is conferred by the formation of a heterotetramer with hGABPβ. In contrast to hGABPα, hGABPβ alone cannot bind to DNA, but it forms a homodimer through its leucine zipper-like structure at the carboxyl terminus and forms a heterodimer with hGABPα through its Notch/ankyrin repeat motif at the amino terminus. The resultant α2β2 heterotetramer has the capacity to activate transcription. Another non-DNA-binding subunit of 47 kDa, E4TF1–47/GABPγ, is structurally identical to hGABPβ except that it differs at its carboxyl extremity and lacks the homodimerization domain. GABPγ retains the ability to form a heterodimer with hGABPα but the resultant αγ heterodimer cannot activate transcription. The subunit composition is therefore one mechanism for the regulation of the transcriptional activity of hGABP (4Sawada J.-i. Goto M. Sawa C. Watanabe H. Handa H. EMBO J. 1994; 13: 1396-1402Crossref PubMed Scopus (46) Google Scholar, 7Sawa C. Goto M. Suzuki F. Watanabe H. Sawada J.-i. Handa H. Nucleic Acids Res. 1996; 24: 4954-4961Crossref PubMed Scopus (47) Google Scholar, 8Suzuki F. Goto M. Sawa C. Ito S. Watanabe H. Sawada J.-i. Handa H. J. Biol. Chem. 1998; 273: 29302-29308Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). In addition to the adenovirus E4 gene and the herpes simplex virus immediate early genes, an increasing number of cellular genes have been found to be targets of E4TF1/hGABP. In accordance with the fact that E4TF1/hGABP is a ubiquitously expressed transcription factor, its targets include ubiquitously expressed genes such as the genes for cytochrome c oxidase subunits IV and Vb (9Virbasius J.V. Virbasius C.A. Scarpulla R.C. Genes Dev. 1993; 7: 380-392Crossref PubMed Scopus (240) Google Scholar), the ATP synthase β-subunit (10Villena J.A. Vinas O. Mampel T. Iglesias R. Giralt M. Villarroya F. Biochem. J. 1998; 331: 121-127Crossref PubMed Scopus (46) Google Scholar), ribosomal proteins L30 and L32 (11Genuario R.R. Kelley D.E. Perry R.P. Gene Expr. 1993; 3: 279-288PubMed Google Scholar), and the retinoblastoma tumor suppressor protein (12Sowa Y. Shiio Y. Fujita T. Matsumoto T. Okuyama Y. Kato D. Inoue J. Sawada J.-i. Goto M. Watanabe H. Handa H. Sakai T. Cancer Res. 1997; 57: 3145-3148PubMed Google Scholar, 13Savoysky E. Mizuno T. Sowa Y. Watanabe H. Sawada J.-i. Nomura H. Ohsugi Y. Handa H. Sakai T. Oncogene. 1994; 9: 1839-1846PubMed Google Scholar). However, some tissue-specific genes, such as male-specific steroid 16α-hydroxylase (14Yokomori N. Kobayashi R. Moore R. Sueyoshi T. Negishi M. Mol. Cell. Biol. 1995; 15: 5355-5362Crossref PubMed Scopus (81) Google Scholar), leukocyte-specific cell adhesion molecule CD18 (β2 integrin) (15Rosmarin A.G. Caprio D.G. Kirsch D.G. Handa H. Simkevich C.P. J. Biol. Chem. 1995; 270: 23627-23633Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar), neutrophil elastase (16Nuchprayoon I. Simkevich C.P. Luo M. Friedman A.D. Rosmarin A.G. Blood. 1997; 89: 4546-4554Crossref PubMed Google Scholar), interleukin-2 (17Avots A. Hoffmeyer A. Flory E. Cimanis A. Rapp U.R. Serfling E. Mol. Cell. Biol. 1997; 17: 4381-4389Crossref PubMed Scopus (46) Google Scholar), utrophin (18Khurana T.S. Rosmarin A.G. Shang J. Krag T.O. Das S. Gammeltoft S. Mol. Biol. Cell. 1999; 10: 2075-2086Crossref PubMed Scopus (104) Google Scholar, 19Gramolini A.O. Angus L.M. Schaeffer L. Burton E.A. Tinsley J.M. Davies K.E. Changeux J.P. Jasmin B.J. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 3223-3227Crossref PubMed Scopus (119) Google Scholar), and nicotinic acetylcholine receptor subunits (20Schaeffer L. Duclert N. Huchet-Dymanus M. Changeux J.P. EMBO J. 1998; 17: 3078-3090Crossref PubMed Scopus (136) Google Scholar), have also been demonstrated to be regulated by E4TF1/hGABP. Despite accumulating evidence for both ubiquitous and tissue-specific gene regulation by E4TF1/hGABP, how this regulation is achieved is still unknown. One of the most likely control mechanisms of such transcriptional regulation is an interaction with other transcription factors. In fact, we and others have demonstrated that E4TF1/hGABP synergistically activates transcription through physical interaction with the ATF1, CREB (21Sawada J.-i. Simizu N. Suzuki F. Sawa C. Goto M. Hasegawa M. Imai T. Watanabe H. Handa H. J. Biol. Chem. 1999; 274: 35475-35482Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar), SP1 (22Rosmarin A.G. Luo M. Caprio D.G. Shang J. Simkevich C.P. J. Biol. Chem. 1998; 273: 13097-13103Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar), SP3 (23Galvagni F. Capo S. Oliviero S. J. Mol. Biol. 2001; 306: 985-996Crossref PubMed Scopus (65) Google Scholar), and HCF transcription factors (24Vogel J.L. Kristie T.M. EMBO J. 2000; 19: 683-690Crossref PubMed Scopus (73) Google Scholar). In contrast, E4TF1/hGABP activity is inhibited by interaction with the mi transcription factor (MITF) in mast cells (25Morii E. Ogihara H. Oboki K. Sawa C. Sakuma T. Nomura S. Esko J.D. Handa H. Kitamura Y. Blood. 2001; 97: 3032-3039Crossref PubMed Scopus (31) Google Scholar). To understand the mechanism of transcriptional regulation by E4TF1/hGABP, it is important to clarify the regulatory cross-talk that occurs with other transcription factors and cofactors. To this end, we screened a cDNA expression library for genes whose products interact with the hGABPβ subunit, and we isolated a cofactor, YEAF1/RYBP. We demonstrate here that YEAF1/RYBP represses the transcriptional activity of E4TF1/hGABP, whereas its close relative, YAF-2 (26Kalenik J.L. Chen D. Bradley M.E. Chen S.J. Lee T.C. Nucleic Acids Res. 1997; 25: 843-849Crossref PubMed Scopus (85) Google Scholar), activates the activity of E4TF1/hGABP. These results provide the first example of a cofactor family with functionally distinct members. A yeast two-hybrid screen was performed using a modified version of the system of Fields and Song (27Fields S. Song O. Nature. 1989; 340: 245-246Crossref PubMed Scopus (4863) Google Scholar). Briefly, pBTM116/hGABPβ-(249–383), encoding a LexA-fusion protein with amino acids 249–383 of hGABPβ, was transformed into the yeast strain L40 by the lithium acetate method. The resultant strain was then transformed with a GAL4-activation domain fusion cDNA library constructed from mRNAs of HeLa cells (MATCHMAKER HL4000AA, CLONTECH). The transformants a for and and at for then in a to and for activity as previously E. Mizuno T. Sowa Y. Watanabe H. Sawada J.-i. Nomura H. Ohsugi Y. Handa H. Sakai T. Oncogene. 1994; 9: 1839-1846PubMed Google Scholar). fusion was from the and yeast and transformed the interaction assay, the L40 yeast strain was transformed with an fusion and GAL4-activation domain fusion and was a transformed then for and activity. three-hybrid assay, was to domain fusion and The expression of the protein can be inhibited by addition of into the fusion GAL4-activation domain fusion for yeast two-hybrid interaction constructed by of into of of A human YY1 cDNA Y. E. T. Cell. 1991; Full Text PDF PubMed Scopus Google Scholar) was a from T. A human YAF-2 cDNA was by a HeLa cDNA library using a YEAF1 cDNA a YEAF1 was from and into to A S-transferase protein was expressed in E. and was then resonance an and the was to the interaction using as previously F. Goto M. Sawa C. Ito S. Watanabe H. Sawada J.-i. Handa H. J. Biol. Chem. 1998; 273: 29302-29308Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). hGABPβ and proteins expressed as previously (3Watanabe H. Sawada J.-i. Yano K. Yamaguchi K. Goto M. Handa H. Mol. Cell. Biol. 1993; 13: 1385-1391Crossref PubMed Scopus (91) Google Scholar). A expression for YEAF1 was constructed by a sequence and YEAF1 cDNA into a of the resultant of which the was into HeLa cells in a using the cells with of The cell was with of for at 4 and the was with The complex was by the in of The and the cell a to a and with using of 2 the assay, and the performed as previously C. Goto M. Suzuki F. Watanabe H. Sawada J.-i. Handa H. Nucleic Acids Res. 1996; 24: 4954-4961Crossref PubMed Scopus (47) Google Scholar). A the human retinoblastoma susceptibility gene promoter and expression for hGABPβ, and hGABPα have also been (12Sowa Y. Shiio Y. Fujita T. Matsumoto T. Okuyama Y. Kato D. Inoue J. Sawada J.-i. Goto M. Watanabe H. Handa H. Sakai T. Cancer Res. 1997; 57: 3145-3148PubMed Google Scholar). The expression in cells for YEAF1, YEAF1 and YAF-2 and constructed by DNA into an expression A human was YEAF1, hGABPβ, and cDNA as by the In order to understand the mechanism of transcriptional regulation by E4TF1/hGABP, it is important to clarify the regulatory cross-talk that occurs with other transcription factors cofactors. We the yeast two-hybrid to screen a cDNA expression library for genes whose products interact with the non-DNA-binding subunit of E4TF1/hGABP We an form of hGABPβ as to interaction with the DNA-binding subunit fusion retains the transactivator and 2 By a HeLa cDNA we of of the and of the revealed that of these a cDNA of in revealed that this was a novel cDNA that to the previously identified YY1-associated factor (26Kalenik J.L. Chen D. Bradley M.E. Chen S.J. Lee T.C. Nucleic Acids Res. 1997; 25: 843-849Crossref PubMed Scopus (85) Google Scholar). By using this cDNA as a and of cDNA we a cDNA of number The cDNA as YY1 and E4TF1/hGABP factor-1 a addition and at the of the cDNA and two at the of its We that the be the it to the of YAF-2 (26Kalenik J.L. Chen D. Bradley M.E. Chen S.J. Lee T.C. Nucleic Acids Res. 1997; 25: 843-849Crossref PubMed Scopus (85) Google Scholar), and its sequence the this and the mRNA from a we that we The YEAF1 protein protein motif other two at its region the protein was to the YAF-2 protein previously (26Kalenik J.L. Chen D. Bradley M.E. Chen S.J. Lee T.C. Nucleic Acids Res. 1997; 25: 843-849Crossref PubMed Scopus (85) Google Scholar). YEAF1 and YAF-2 the at the domain the two and at the which we to as conserved region and YEAF1 also contains a unique region and that is in and we to this as the YEAF1 original region YEAF1 was found to be highly to E. C. M. M. EMBO J. 1999; PubMed Scopus Google Scholar), indicating that YEAF1 and are binding of YEAF1 to hGABPβ was by the yeast two-hybrid as by and by and A fusion protein interacted with a fusion protein of hGABPβ and an that was as for two-hybrid indicating that the repeat for interaction with hGABPα are for interaction with A with YEAF1 the leucine zipper-like structure for homodimerization and These results that a region of hGABPβ amino acids is for with an form of hGABPβ that retains this region but lacks the to form homodimer and to was to interact with In contrast, the fusion of the DNA-binding subunit hGABPα interact with it interact with we an interaction of YEAF1 with the transcription factor with the and of These results that YEAF1 with hGABPβ. We also found that YEAF1 with YY1 2 as be its to which was originally identified as an interacting partner of YY1 (26Kalenik J.L. Chen D. Bradley M.E. Chen S.J. Lee T.C. Nucleic Acids Res. 1997; 25: 843-849Crossref PubMed Scopus (85) Google Scholar). YEAF1 with both hGABPβ and these we this protein YEAF1 YY1- We the domain of YEAF1 that is for with hGABPβ. A of of YEAF1 to and for interaction with in yeast was by both and by the conserved region 2 of YEAF1 was for interaction with hGABPβ. The fact that the of YEAF1 has sequence with the region of YAF-2 to the interaction of YAF-2 and hGABPβ. we to the interaction of the and fusion proteins by a yeast two-hybrid YEAF1 and YAF-2 constitute a protein family that with the hGABP transcription factor. We the of the hGABPβ and YEAF1 interaction using surface plasmon resonance A purified fusion protein with YEAF1 was the surface a previously By purified hGABPβ protein at into the control we at the and of interaction of hGABPβ and A the by the The interaction of hGABPβ and YEAF1 was indicating that hGABPβ and YEAF1 bind in these the a and of the interaction 4 and are in 4 with previously using hGABPβ and hGABPα F. Goto M. Sawa C. Ito S. Watanabe H. Sawada J.-i. Handa H. J. Biol. Chem. 1998; 273: 29302-29308Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). The of hGABPβ and YEAF1 was which is the for the hGABPβ and hGABPα subunits. We also the interaction and YEAF1 in a and we a 4 and To YEAF1 forms a complex with hGABPβ YY1 in vivo, we first constructed an expression YEAF1 protein and the into HeLa of the cells with an revealed that the protein is in the was using cells with a YEAF1 expression the and of YEAF1 both hGABP and YY1 are transcription factors. We then from the cells and to using the of the by with and in both hGABPβ and YY1 in the but in the control that YEAF1 forms a complex with both hGABPβ and YY1 in the The that hGABP, YEAF1, and YY1 form a To this we performed a yeast three-hybrid in A. In addition to the and fusion the protein is expressed in yeast to a complex The expression of the protein can be by addition of into the The activity was hGABPβ was to the and we evidence for interaction of the with the of an YEAF1 protein in and of the YEAF1 expression by addition of in of the activity 2 and These results that these proteins form a complex in We that hGABPα, hGABPβ, and YEAF1 form a complex These results that hGABPα, hGABPβ, YEAF1, and YY1 form a and YEAF1 as a bridging factor of the hGABP and YY1 transcription factors. We the of YEAF1 and YAF-2 the activity of To this end, we transcriptional activity of hGABP by and a We a human retinoblastoma gene as a and the D. 2 cell as a the promoter contains an (12Sowa Y. Shiio Y. Fujita T. Matsumoto T. Okuyama Y. Kato D. Inoue J. Sawada J.-i. Goto M. Watanabe H. Handa H. Sakai T. Cancer Res. 1997; 57: 3145-3148PubMed Google Scholar, 13Savoysky E. Mizuno T. Sowa Y. Watanabe H. Sawada J.-i. Nomura H. Ohsugi Y. Handa H. Sakai T. Oncogene. 1994; 9: 1839-1846PubMed Google Scholar), and cells activity C. Goto M. Suzuki F. Watanabe H. Sawada J.-i. Handa H. Nucleic Acids Res. 1996; 24: 4954-4961Crossref PubMed Scopus (47) Google Scholar). we have previously C. Goto M. Suzuki F. Watanabe H. Sawada J.-i. Handa H. Nucleic Acids Res. 1996; 24: 4954-4961Crossref PubMed Scopus (47) Google Scholar), of an expression the DNA-binding subunit hGABPα alone activity whereas of the hGABPβ subunit the in of activity and of an increasing of YEAF1 expression with hGABPα and hGABPβ in a of activity and indicating that YEAF1 as a transcriptional The was a YEAF1 in hGABPβ binding was and we an of the activity. for this be In contrast to YEAF1, the transcriptional activity of hGABP was by of an increasing of indicating that YAF-2 as a transcriptional for hGABP YEAF1 and YAF-2 the transcriptional activity of hGABP, structurally We mRNA expression of YEAF1, YAF-2 in using DNA mRNA of was in the we with the expression in with a that YAF-2 is expressed in cells (26Kalenik J.L. Chen D. Bradley M.E. Chen S.J. Lee T.C. Nucleic Acids Res. 1997; 25: 843-849Crossref PubMed Scopus (85) Google Scholar), YAF-2 mRNA expression was the in and skeletal we previously F. Goto M. Sawa C. Ito S. Watanabe H. Sawada J.-i. Handa H. J. Biol. Chem. 1998; 273: 29302-29308Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar), hGABPβ mRNA was expressed ubiquitously The expression mRNA was the in and skeletal muscle, YEAF1 YAF-2 mRNA also highly expression is these results the that YEAF1 and YAF-2 are tissue-specific cofactors for the hGABP transcription factor. In this we the and of YEAF1, a novel of the hGABP/E4TF1 transcription factor. We demonstrated that YEAF1 and its close YAF-2 also interact with transcription factor YY1 and that as bridging factors for and Despite their similarity, YEAF1 and YAF-2 functionally in that YEAF1 negatively regulated the transcriptional activity of hGABP but YAF-2 positively regulated the activity. We demonstrated here that YEAF1 and YAF-2 constitute a family of cofactors for the hGABP and YY1 transcription factors. The first identified was originally isolated as a factor interacting with YY1 in yeast two-hybrid (26Kalenik J.L. Chen D. Bradley M.E. Chen S.J. Lee T.C. Nucleic Acids Res. 1997; 25: 843-849Crossref PubMed Scopus (85) Google Scholar). from their sequence similarity, we that YEAF1 also with and YAF-2 with hGABPβ. We other family of YEAF1 and YAF-2 in a of the human using the but we genes, in the D. T. F. S. M. H. J.-i. K. and H. that are conserved at YEAF1 is the human homologue of the was isolated as an interacting partner of a of the Polycomb group of proteins E. C. M. M. EMBO J. 1999; PubMed Scopus Google Scholar). The proteins form that are for the of the of a number of It has been that also with a homologue of and with YY1 E. C. M. M. EMBO J. 1999; PubMed Scopus Google Scholar). YY1 has to the gene J.L. D. M. J.A. Mol. Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), and accumulating evidence that YY1 is also in function E. C. M. M. EMBO J. 1999; PubMed Scopus Google Scholar, J. Mol. Cell. Biol. 2001; PubMed Scopus Google Scholar). is to be a of and as a transcriptional with the DNA-binding domain of the transcription factor E. C. M. M. EMBO J. 1999; PubMed Scopus Google Scholar). The most of the function of YEAF1/RYBP is that is by the J.M. J. J.A. Proc. Natl. Acad. Sci. U. S. A. 2001; PubMed Scopus Google Scholar) that with the domain of a related of the transcription factors. has been to form with other proteins such as and We demonstrated here that YEAF1 binds to hGABP and represses its transcriptional activity. YEAF1/RYBP the transcriptional of at two sequence-specific DNA-binding and YY1 also be the of YEAF1 YY1 can as a transcriptional the promoter It that represses transcription by interacting with In contrast to and such an function domain has been to hGABPβ. the YEAF1 interaction domain of hGABPβ with the transactivator a domain an domain. YEAF1 be to to hGABP and the transcriptional activity of hGABP by with such as for binding to These two mechanisms are and is to understand the molecular mechanism of transcriptional by Despite the of YEAF1 and YAF-2 for hGABPβ, YAF-2 hGABP transcriptional activity and YEAF1 as we YEAF1 and YAF-2 are the only structurally related transcriptional cofactors that have It has been that the of and are for transcriptional YAF-2 the ability to transcription it lacks the and its region is this is the one for the of YEAF1 and YAF-2 is that YAF-2 lacks the ability to bind to YAF-2 have an domain. It be that with hGABP of a YEAF1 protein that lacks and the ability to bind to hGABP in an of promoter activity YEAF1 for binding to YEAF1 with which to of and to the of transcriptional activity. We that both hGABP, YEAF1, and YY1 form a both hGABP and YY1 are sequence-specific DNA-binding YEAF1 be to hGABP and YY1 bind to It is that some binding for both the hGABP and YY1 transcription factors. the promoter of the human contains and I. U. Y. Sawa C. Handa H. L. F. J. Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus Google Scholar). The activity of this promoter was by hGABP and by YEAF1/RYBP is a of E. C. M. M. EMBO J. 1999; PubMed Scopus Google Scholar), binding of YY1 to the promoter YEAF1 and to hGABP, which in transcriptional be the for oxidase subunit genes N. C. J. Nucleic Acids Res. Mol. Biol. 1998; PubMed Google Scholar), whose promoter also binding for hGABP and but both of which in this have been to be for transcription. One can speculate that bridging by YAF-2 transcription by hGABP and However, a of the regulation of such is to understand the mechanism of and regulation by hGABP and and of the functionally distinct bridging factors YEAF1 and YAF-2 here the molecular mechanisms of transcriptional regulation by hGABP and as as by We are to S. M. for of the yeast and the and its and to T. for with the yeast We T. for the of YY1 We also T. Wada and T. Imai for and