Specific Interaction of TAFII105 with OCA-B Is Involved in Activation of Octamer-dependent Transcription

TAFII105 is a TFIID-associated factor highly expressed in B lymphocytes. This subunit is found in a small portion of TFIID complexes and is homologous to human TAFII130 and Drosophila TAFII110. In the present study we show that TAFII105 is involved in transcription activation directed by the B cell-specific octamer element found in many B cell-specific genes. B cells overexpressing TAFII105 display higher octamer-dependent transcription, whereas expression of a C-terminal truncated form of TAFII105 inhibits octamer transcription in a dominant negative manner. In addition, antibodies directed against TAFII105 specifically inhibit octamer-dependent transcription. Reporter gene analysis revealed that TAFII105 elevates octamer transcription in the presence of OCA-B, a cofactor subunit of Oct1 and Oct2 proteins. In vitro binding assays and functional studies established that the effect of TAFII105 on octamer activity involves interaction of TAFII105 with octamer-binding complexes via the C-terminal activation domain of OCA-B. These findings link TAFII105 coactivator function to B cell-specific transcription. TAFII105 is a TFIID-associated factor highly expressed in B lymphocytes. This subunit is found in a small portion of TFIID complexes and is homologous to human TAFII130 and Drosophila TAFII110. In the present study we show that TAFII105 is involved in transcription activation directed by the B cell-specific octamer element found in many B cell-specific genes. B cells overexpressing TAFII105 display higher octamer-dependent transcription, whereas expression of a C-terminal truncated form of TAFII105 inhibits octamer transcription in a dominant negative manner. In addition, antibodies directed against TAFII105 specifically inhibit octamer-dependent transcription. Reporter gene analysis revealed that TAFII105 elevates octamer transcription in the presence of OCA-B, a cofactor subunit of Oct1 and Oct2 proteins. In vitro binding assays and functional studies established that the effect of TAFII105 on octamer activity involves interaction of TAFII105 with octamer-binding complexes via the C-terminal activation domain of OCA-B. These findings link TAFII105 coactivator function to B cell-specific transcription. TATA-binding protein associated factor major late promoter polymerase chain reaction glutathione S-transferase hemagglutinin The program of B cell-specific gene expression during development is highly controlled and is governed by gene-specific organization of DNA regulatory elements and combinatorial interactions of ubiquitous and cell type-specific transcription factors and cofactors. In recent years significant progress has been made in identifying and understanding the physiological role of transcription factors involved in B cell development (1.Henderson A. Calame K. Annu. Rev. Immunol. 1998; 16: 163-200Crossref PubMed Scopus (112) Google Scholar). However, much less is known about the mechanism underlying the transcription activation process by these factors. Considering the accumulating evidence indicating that interactions of activators with various components of the general transcription apparatus are essential for transcription activation process, it is reasonable that similar mechanisms apply also for B cell transcription factors. Several studies implicated the basal transcription factor TFIID as potential target for specific activation domains of activators (2.Pugh B.F. Tjian R. Cell. 1990; 61: 1187-1197Abstract Full Text PDF PubMed Scopus (736) Google Scholar, 3.Horikoshi M. Wang C.K. Fujii H. Cromlish J.A. Weil P.A. Roeder R.G. Proc. Natl. Acad. Sci. U. S. A. 1989; 86: 4843-4847Crossref PubMed Scopus (58) Google Scholar). TFIID is a multiprotein complex consisting of TATA-binding protein (TBP) and associated factors, TAFs1 (4.Dynlacht B.D. Hoey T. Tjian R. Cell. 1991; 66: 563-576Abstract Full Text PDF PubMed Scopus (485) Google Scholar, 5.Tanese N. Pugh B.F. Tjian R. Genes Dev. 1991; 5: 2212-2224Crossref PubMed Scopus (244) Google Scholar, 6.Zhou Q. Lieberman P.M. Boyer T.G. Berk A.J. Genes Dev. 1992; 6: 1964-1974Crossref PubMed Scopus (289) Google Scholar, 7.Poon D. Weil P.A. J. Biol. Chem. 1993; 268: 15325-15328Abstract Full Text PDF PubMed Google Scholar, 8.Reese J.C. Apone L. Walker S.S. Griffin L.A. Green M.R. Nature. 1994; 371: 523-527Crossref PubMed Scopus (148) Google Scholar). TFIID is required for directing core promoter recognition and pre-initiation complex assembly (9.Verrijzer C.P. Tjian R. Trends Biochem. Sci. 1996; 21: 338-342Crossref PubMed Scopus (319) Google Scholar, 10.Hoffmann A. Oelgeschlager T. Roeder R.G. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 8928-8935Crossref PubMed Scopus (77) Google Scholar). In vitro transcription studies have indicated that the TAF subunits play a crucial role as activation domain mediators (coactivators) through direct interaction with activators (11.Chen J.L. Attardi L. Verrijzer C.P. Yokomori K. Tjian R. Cell. 1994; 79: 93-105Abstract Full Text PDF PubMed Scopus (328) Google Scholar, 12.Thut C.J. Chen J.L. Klemm R. Tjian R. Science. 1995; 267: 100-104Crossref PubMed Scopus (407) Google Scholar, 13.Sauer F. Hansen S.K. Tjian R. Science. 1995; 270: 1783-1788Crossref PubMed Scopus (168) Google Scholar). In addition, certain TAFs also function as promoter selectivity factors (14.Verrijzer C.P. Chen J.L. Yokomori K. Tjian R. Cell. 1995; 81: 1115-1125Abstract Full Text PDF PubMed Scopus (257) Google Scholar, 15.Burke T.W. Kadonada J.T. Genes Dev. 1996; 10: 711-724Crossref PubMed Scopus (328) Google Scholar). Several reports suggested that certain TAFs play an important role in gene-specific transcriptional activation in vivo in high eukaryotes (16.May M. Mengus G. Lavigne A.C. Chambon P. Davidson I. EMBO J. 1996; 15: 3093-3104Crossref PubMed Scopus (76) Google Scholar, 17.Mengus G. May M. Carry L. Chambon P. Davidson I. Genes Dev. 1997; 11: 1381-1395Crossref PubMed Scopus (134) Google Scholar, 18.Wang E.H. Zou S. Tjian R. Genes Dev. 1997; 11: 2658-2669Crossref PubMed Scopus (78) Google Scholar, 19.Yamit-Hezi A. Dikstein R. EMBO J. 1998; 17: 5161-5169Crossref PubMed Scopus (69) Google Scholar, 20.Zhou J. Zwicker J. Szymanski P. Levine M. Tjian R. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13483-13488Crossref PubMed Scopus (62) Google Scholar). Recent genetic experiments in yeast with individual TAF mutants suggested that, whereas some TAFs are essential for transcription of the majority of class II genes (21.Apone L.M. Virbasius C.A. Holstege F.C. Wang J. Young R.A. Green M.R. Mol. Cell. 1998; 2: 653-661Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 22.Michel B. Komarnitsky P. Buratowski S. Mol. Cell. 1998; 2: 663-673Abstract Full Text Full Text PDF PubMed Scopus (93) Google Scholar, 23.Moqtaderi Z. Keaveney M. Struhl K. Mol. Cell. 1998; 2: 675-682Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar, 24.Natarajan K. Jackson B.M. Rhee E. Hinnebusch A.G. Mol. Cell. 1998; 2: 683-692Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar, 25.Sanders S.L. Klebanow E.R. Weil P.A. J. Biol. Chem. 1999; 274: 18847-18850Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar, 26.Komarnitsky P.B. Michel B. Buratowski S. Genes Dev. 1999; 13: 2484-2489Crossref PubMed Scopus (53) Google Scholar), certain TAFs are not generally required for transcription activation (27.Apone L.M. Virbasius C.M.A. Reese J.C. Green M.R. Genes Dev. 1996; 10: 2368-2380Crossref PubMed Scopus (130) Google Scholar, 28.Moqtaderi Z. Bai Y. Poon D. Weil P.A. Struhl K. Nature. 1996; 383: 188-191Crossref PubMed Scopus (251) Google Scholar, 29.Walker S.S. Reese J.C. Apone L.M. Green M.R. Nature. 1996; 383: 185-188Crossref PubMed Scopus (213) Google Scholar). Due to a lack of additional genetic studies in metazoans, little is known about the transcription regulatory pathways that specifically require the activities of the TAFs. Previously we have cloned a subunit of TFIID, TAFII105, that is related to the coactivator subunit hTAFII130 and toDrosophila TAFII110 (30.Dikstein R. Zhou S. Tjian T. Cell. 1996; 87: 137-146Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). The C-terminal third of these subunits is highly conserved (17.Mengus G. May M. Carry L. Chambon P. Davidson I. Genes Dev. 1997; 11: 1381-1395Crossref PubMed Scopus (134) Google Scholar, 30.Dikstein R. Zhou S. Tjian T. Cell. 1996; 87: 137-146Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). The N terminus of TAFII105 is significantly more diverged and was shown to be involved in interaction with activation domains of activators (19.Yamit-Hezi A. Dikstein R. EMBO J. 1998; 17: 5161-5169Crossref PubMed Scopus (69) Google Scholar). Unlike most TAF subunits that are conserved from yeast to human, no homolog has been found for the family of hTAFII105, hTAFII130, and dTAFII110 proteins in yeast, suggesting that these TAFs might be involved in transcription regulatory pathways that do not exist in yeast. TAFII105 was originally identified as TFIID-associated polypeptide that is highly abundant in purified TFIID complex isolated from mature B cell line (30.Dikstein R. Zhou S. Tjian T. Cell. 1996; 87: 137-146Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). Because the expression pattern of a transcription factor usually correlates with its function, it was postulated that TAFII105 may be involved in B cell-specific transcription (30.Dikstein R. Zhou S. Tjian T. Cell. 1996; 87: 137-146Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). TAFII105 appears to be present only in a subset of TFIID complexes, and therefore is likely to function in the context of a specific set of genes. Consistent with these assumptions, our previous analysis of TAFII105 function revealed that it acts as an activation domain-specific coactivator of p65/RelA, a subunit of the NF-κB family of transcription factors (19.Yamit-Hezi A. Dikstein R. EMBO J. 1998; 17: 5161-5169Crossref PubMed Scopus (69) Google Scholar). These studies also indicated that the p65·TAFII105 complex is involved in cytokine-mediated gene expression and anti-apoptotic gene activation (19.Yamit-Hezi A. Dikstein R. EMBO J. 1998; 17: 5161-5169Crossref PubMed Scopus (69) Google Scholar). In the present study we investigated the role of TAFII105 in transcription regulation mediated by the octamer motif. The octamer motif plays a crucial role in directing the B cell-specific expression of immunoglobulin and other B cell-specific genes. This motif is found in the promoters and enhancers of all immunoglobulin genes and is essential for the B cell-specific expression of these genes (31.Staudt L.M. Lenardo M.J. Annu. Rev. Immunol. 1991; 9: 373-398Crossref PubMed Scopus (244) Google Scholar). Two octamer-binding factors are expressed in B cells, a ubiquitous protein Oct1 and the B cell-specific factor Oct2. These proteins associate with a B cell-specific cofactor OCA-B also known as OBF-1 and Bob1 (32.Gstaiger M. Knoepfel L. Georgiev O. Schaffner W. Hovens C.M. Nature. 1995; 373: 360-362Crossref PubMed Scopus (285) Google Scholar, 33.Luo Y. Roeder R.G. Mol. Cell. Biol. 1995; 15: 4115-4124Crossref PubMed Scopus (250) Google Scholar, 34.Strubin M. Newell J.M. Mattias P. Cell. 1995; 80: 497-506Abstract Full Text PDF PubMed Scopus (351) Google Scholar). OCA-B interacts with Oct1 and Oct2 via its N terminus and provides a strong activation domain to this complex. Our studies reveal that TAFII105 plays a transcription coactivator role required for a high level of B cell-specific octamer activity. Dissection of the molecular mechanism involved in the effect of TAFII105 on octamer transcription revealed that TAFII105 interacts with octamer-binding complexes through direct interaction with the cofactor OCA-B. This interaction is required for TAFII105 enhancement of octamer-dependent activity and is mediated by the C-terminal activation domain of OCA-B and the coactivation domain of TAFII105. These results suggest that TAFII105 is an additional regulatory component of octamer-dependent B cell-specific gene expression, acting as coactivator for octamer-binding complexes. For the in vitro transcription reactions we used nuclear extract prepared from the B cell line Daudi. The reaction mixture (18 μl) contained 3 μl of extract, 6 μl of transcription buffer (20 mm Hepes, pH 7.9; 100 mm KCl; 2 mm MgCl2; 0.2 mm EDTA; 20% glycerol; and 1 mm dithiothreitol), 0.6 μl of 0.1m MgCl2, 40 units of RNasin, and 200 ng of DNA template. The reaction was for 2 μl of the mixture was and mm and 1 and 100 and for the major late promoter mm and and 100 and the reaction was for additional The reaction was by 200 μl of mixture mm EDTA; mm pH and and and on a antibodies used in the with the transcription mixture in the of the DNA for by the antibodies used in the transcription are antibodies directed against (30.Dikstein R. Zhou S. Tjian T. Cell. 1996; 87: 137-146Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). The core antibodies by OCA-B was by polymerase chain reaction a cell and the For in vitro transcription and of OCA-B, the was by and was cloned of a The of the was and found to be expression for OCA-B was in from was of to a nuclear and from this was of M. W. Cell. 1990; Full Text PDF PubMed Scopus Google Scholar). TAFII105 expression was by an and a from of TAFII105 expression was a from the and from the for TAFII105, of a was by from (30.Dikstein R. Zhou S. Tjian T. Cell. 1996; 87: 137-146Abstract Full Text Full Text PDF PubMed Scopus (159) Google the of to was by and was used as a with the The was of the by of to was cloned by the and of The was cloned and the in the The was by a a octamer motif as to a core promoter to of as and The was by an from of was by from of The and a from T. The chain was by the late M. and the was (30.Dikstein R. Zhou S. Tjian T. Cell. 1996; 87: 137-146Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). The used for in was by and The and the OCA-B was with by a with and the was of the was by an of on the of proteins be by The N and of TAFII105, and TAFII130 expressed as a protein in The proteins purified and on and various proteins in vitro polymerase and and with the proteins in buffer (20 mm Hepes, pH 7.9; 100 mm KCl; mm MgCl2; 0.2 mm EDTA; 1 mm 0.2 for 2 The with the buffer and with The proteins by for in protein buffer by and extract from cells was prepared as (30.Dikstein R. Zhou S. Tjian T. Cell. 1996; 87: 137-146Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). μl of nuclear extract in with with as the proteins with an and by and antibodies cells in with the For cells with the indicated in a a of of usually 100 ng of the ng of and 200 ng of The of in was mature B cells in with to TAFII105 to the of in a of of in the effect of dominant negative TAFII105, a was 3 of and of The of in was of cells TAFII105 was in TAFII105 in cells a of 1 cells in was with of DNA and a the cells the the was with a was and through a cells with the 2 of the and used to for an additional of was to for an additional of the component is was of cells by the a in the of TAFII105 in octamer-dependent transcription, we established a of B cells These and cells with octamer-dependent genes 1 octamer and the other has a octamer to a core promoter shown in octamer-dependent activity is higher in The activities of octamer octamer motif and by TAFII105 expression the of of octamer activity was not it was highly Considering the results shown in the it may be by the level of expression TAFII105 in cells to human cells we the potential of a C-terminal truncated form of TAFII105 to inhibit octamer transcription. This is of the C-terminal domain and was shown to as a dominant negative of TAFII105 function (19.Yamit-Hezi A. Dikstein R. EMBO J. 1998; 17: 5161-5169Crossref PubMed Scopus (69) Google Scholar). and B cell with octamer-dependent with expression for shown in 1 octamer transcription in cell more the of TAFII105 in octamer-dependent transcription, we in vitro transcription reactions a of octamer elements of a core promoter and nuclear extract prepared from the B cell the transcription level of the was significantly higher the core promoter 1 1 and that octamer-binding proteins octamer transcription in directed against TAFII105 domain of octamer-dependent transcription 2 and whereas antibodies have no effect on octamer transcription 2 and less was on transcription mediated by the major late core with our previous that of the TFIID TAFII105 in nuclear extract these results suggest that TAFII105 is involved in transcription in B In B cells, gene activation through an octamer motif is by binding proteins Oct1 and Oct2 and a B cell-specific cofactor OCA-B P. Immunol. 1998; 10: PubMed Scopus Google Scholar). OCA-B is to the octamer by direct interaction with the domains of Oct1 and Oct2 and transcription by a transcription activation function to Oct1 and Oct2 (32.Gstaiger M. Knoepfel L. Georgiev O. Schaffner W. Hovens C.M. Nature. 1995; 373: 360-362Crossref PubMed Scopus (285) Google Scholar, 33.Luo Y. Roeder R.G. Mol. Cell. Biol. 1995; 15: 4115-4124Crossref PubMed Scopus (250) Google Scholar, 34.Strubin M. Newell J.M. Mattias P. Cell. 1995; 80: 497-506Abstract Full Text PDF PubMed Scopus (351) Google Scholar). the role of TAFII105 in transcription, the effect of OCA-B and TAFII105 expression on octamer-dependent transcription activity was experiments in the human cell line In these cells OCA-B is to the promoter by the expressed Oct1 a core promoter element and an octamer with OCA-B TAFII105 expression and activity was a coactivation effect by we used of shown in expression of TAFII105 and OCA-B in a of octamer activity to the expression of of these proteins with 2 This is specific of a TFIID subunit related to TAFII105, has no effect on octamer activity not TAFII105 to the octamer in the presence of OCA-B the that TAFII105 core promoter the role of TAFII105 in transcription of we used a gene by promoters of B cell-specific immunoglobulin chain and The promoter of genes an octamer the promoter activity of these genes in cells is B of OCA-B TAFII105 with these has effect on and chain promoter activities B and 2 and However, of OCA-B and TAFII105 with the B cell-specific genes in strong of gene suggesting that OCA-B and TAFII105 to the activity of these The of OCA-B activity by TAFII105 in the context of the promoters is that with the promoter 2 the that the organization of the promoters is more for activation by OCA-B and TAFII105. these results suggest that TAFII105 coactivator function on the octamer element is mediated by OCA-B. the mechanism involved in TAFII105 on octamer transcription, we octamer factors with TAFII105. For this nuclear extract prepared from the B cell line was with TAFII105 and the proteins by antibodies specific to Oct2 and OCA-B. shown in Oct2 and OCA-B on not on The binding of Oct2 and OCA-B is specific B cell transcription to associate with on the Because OCA-B is in B cells with Oct1 and we of these proteins to TAFII105. of the proteins and OCA-B was in vitro in and used for binding with C-terminal of TAFII105. shown in 3 the proteins only OCA-B specifically and interacts with the domain of TAFII105. The binding of OCA-B to the TAFII105 N terminus is specific it not with protein from the N terminus of hTAFII130 3 is with the level of TAFII105 and TAFII130 this Considering the of octamer activity in B cells by a C-terminal truncated form of TAFII105 1 and the direct of OCA-B with this it is reasonable to that this its effect by with TAFII105 protein for OCA-B evidence that the effect of TAFII105 on octamer-dependent transcription is mediated by OCA-B, we have a of OCA-B the and it for TAFII105 binding and transcription activity. shown in of the significantly TAFII105 This is of octamer transcription in cells Consistent with TAFII105 binding of TAFII105 with the OCA-B to its activity These results suggest that the interaction TAFII105 and OCA-B is important for activation of octamer-dependent transcription. studies have indicated that OCA-B transcription activation domain is to and the domain the C-terminal M. Georgiev O. H. P. Schaffner W. EMBO J. 1996; 15: PubMed Scopus Google Scholar, P. S. J. T. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar, Y. H. S. H. Roeder R.G. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). of the activation domains is involved in TAFII105 coactivation function and to that OCA-B TAFII105 OCA-B domains to the yeast DNA binding domain These proteins with gene by to a core DNA binding domain transcription activity and is not by TAFII105 3 OCA-B mutants and not the activity and suggesting that the of of OCA-B are crucial for the activation However, these C-terminal truncated proteins are not to TAFII105 expression and of OCA-B also a strong activation domain The activity of this is by TAFII105 expression that coactivation by TAFII105 is mediated by the C-terminal activation OCA-B is in the context of with whereas it is in the context of the the that the activation domain of OCA-B is and in the analysis of B cell-specific transcription regulation by the octamer motif revealed the of octamer-binding factors, the ubiquitous Oct1 and the B Oct2. These factors are not to a high level of octamer activity in B This activity is by OCA-B, a B cell-specific cofactor OBF-1 and that is specifically to octamer by the Oct1 and Oct2 proteins (32.Gstaiger M. Knoepfel L. Georgiev O. Schaffner W. Hovens C.M. Nature. 1995; 373: 360-362Crossref PubMed Scopus (285) Google Scholar, 33.Luo Y. Roeder R.G. Mol. Cell. Biol. 1995; 15: 4115-4124Crossref PubMed Scopus (250) Google Scholar, 34.Strubin M. Newell J.M. Mattias P. Cell. 1995; 80: 497-506Abstract Full Text PDF PubMed Scopus (351) Google Scholar). In the present study we evidence that octamer-dependent activity in B cells is more complex and also involves the B TFIID subunit TAFII105 as transcription coactivator for octamer-binding complexes. in vitro transcription studies we show that transcription, with B cell nuclear extract, is interaction assays and gene analysis revealed that OCA-B not Oct1 Oct2 TAFII105 and that this interaction is essential for of octamer activity. we show that OCA-B and TAFII105 is more on B cell-specific promoters the octamer motif. Consistent with a coactivator this interaction is mediated by the OCA-B activation domain and the coactivation domain of TAFII105. the high of OCA-B and in the of B these proteins are likely to associate and the transcription of specific target genes in B Because OCA-B transcription in B cells only through octamer P. S. J. T. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar), it be to TAFII105 is also involved in transcription activation of a octamer motif that Oct2 and B cofactor T. P. A. S. H. 1995; PubMed Scopus Google Scholar). Unlike core TFIID-associated factors, TAFII105 is found in a small portion of TFIID complexes, in certain mature B cell and in cells (30.Dikstein R. Zhou S. Tjian T. Cell. 1996; 87: 137-146Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). TFIID is likely to be involved in transcription regulation of small of genes. that the of TFIID in the cell is activators of TAFII105 binding might have an in for TFIID and more to gene This is important for genes that be and highly as immunoglobulin genes as we have anti-apoptotic genes (19.Yamit-Hezi A. Dikstein R. EMBO J. 1998; 17: 5161-5169Crossref PubMed Scopus (69) Google Scholar). The C-terminal of OCA-B an activation domain crucial for OCA-B of this the of OCA-B to octamer-dependent transcription. This is similar to an in of this significantly OCA-B activity in vitro and in cells Y. H. S. H. Roeder R.G. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). Consistent with the that direct interaction TAFII105 and OCA-B is involved in octamer transcription in TAFII105 to transcription activation by the OCA-B protein the C-terminal domain and to this the C-terminal activation activation domain OCA-B was identified and to M. Georgiev O. H. P. Schaffner W. EMBO J. 1996; 15: PubMed Scopus Google Scholar, P. S. J. T. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). Our studies revealed that the activation domain is not by TAFII105. the of the of OCA-B to transcription and the that C-terminal of OCA-B M. Georgiev O. H. P. Schaffner W. EMBO J. 1996; 15: PubMed Scopus Google as as C-terminal truncated protein of OCA-B and are it is that the an activation analysis of OCA-B activity revealed that the component is required for transcription activation by OCA-B in a purified transcription Y. H. S. H. Roeder R.G. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). In addition, a nuclear extract, these also revealed the of an additional and OCA-B coactivator activity. be that of TAFII105 and OCA-B for transcriptional activation in cells was not not These findings with the present study that OCA-B pathways for transcription activation in cell is also that in some OCA-B might during of the transcription activation Consistent with this is the that the coactivation function of is on TAFs S. M. Roeder R.G. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar, C.M. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). in vitro transcription studies indicated that TAFs are required for transcription activation (9.Verrijzer C.P. Tjian R. Trends Biochem. Sci. 1996; 21: 338-342Crossref PubMed Scopus (319) Google Scholar, 10.Hoffmann A. Oelgeschlager T. Roeder R.G. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 8928-8935Crossref PubMed Scopus (77) Google Scholar). However, recent studies revealed a mechanism of transcription activation that is A.J. Young R.A. Nature. 1994; PubMed Scopus Google Scholar, T. Y. Roeder R.G. Mol. Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). The of transcription activation pathways with coactivator activities the that in gene-specific regulation is by the combinatorial of of therefore an additional level of