Crystal Structure of the Human BRD2 Bromodomain

Abstract

The BET (bromodomains and extra terminal domain) family proteins recognize acetylated chromatin through their bromodomain and act as transcriptional activators. One of the BET proteins, BRD2, associates with the transcription factor E2F, the mediator components CDK8 and TRAP220, and RNA polymerase II, as well as with acetylated chromatin during mitosis. BRD2 contains two bromodomains (BD1 and BD2), which are considered to be responsible for binding to acetylated chromatin. The BRD2 protein specifically recognizes the histone H4 tail acetylated at Lys12. Here, we report the crystal structure of the N-terminal bromodomain (BD1, residues 74-194) of human BRD2. Strikingly, the BRD2 BD1 protein forms an intact dimer in the crystal. This is the first observation of a homodimer among the known bromodomain structures, through the buried hydrophobic core region at the interface. Biochemical studies also demonstrated BRD2 BD1 dimer formation in solution. The two acetyllysine-binding pockets and a negatively charged secondary binding pocket, produced at the dimer interface in BRD2 BD1, may be the unique features that allow BRD2 BD1 to selectively bind to the acetylated H4 tail. The BET (bromodomains and extra terminal domain) family proteins recognize acetylated chromatin through their bromodomain and act as transcriptional activators. One of the BET proteins, BRD2, associates with the transcription factor E2F, the mediator components CDK8 and TRAP220, and RNA polymerase II, as well as with acetylated chromatin during mitosis. BRD2 contains two bromodomains (BD1 and BD2), which are considered to be responsible for binding to acetylated chromatin. The BRD2 protein specifically recognizes the histone H4 tail acetylated at Lys12. Here, we report the crystal structure of the N-terminal bromodomain (BD1, residues 74-194) of human BRD2. Strikingly, the BRD2 BD1 protein forms an intact dimer in the crystal. This is the first observation of a homodimer among the known bromodomain structures, through the buried hydrophobic core region at the interface. Biochemical studies also demonstrated BRD2 BD1 dimer formation in solution. The two acetyllysine-binding pockets and a negatively charged secondary binding pocket, produced at the dimer interface in BRD2 BD1, may be the unique features that allow BRD2 BD1 to selectively bind to the acetylated H4 tail. The eukaryotic genome forms a polymeric structure consisting of repetitive units of nucleosomes (1Kornberg R.D. Lorch Y. Cell. 1999; 98: 285-294Abstract Full Text Full Text PDF PubMed Scopus (1464) Google Scholar). In each nucleosome, the DNA is wrapped around an octamer of core histones: two H2A/H2B dimers and an H3/H4 tetramer (2Luger K. Mader A.W. Richmond R.K. Sargent D.F. Richmond T.J. Nature. 1997; 389: 251-260Crossref PubMed Scopus (7141) Google Scholar). All of the core histones are basic proteins comprising N- and C-terminal tail regions and a central core domain. The N-terminal tail regions are rich in lysine and, to a lesser extent, arginine and serine. The tail regions are assumed to be flexible in the nucleosome, thus allowing access to enzymes such as acetyltransferases, methyltransferases, and kinases for covalent modifications (3Rice J.C. Allis C.D. Curr. Opin. Cell Biol. 2001; 13: 263-273Crossref PubMed Scopus (578) Google Scholar, 4Roth S.Y. Denu J.M. Allis C.D. Annu. Rev. Biochem. 2001; 70: 81-120Crossref PubMed Scopus (1660) Google Scholar). The histone code, which is defined by covalent modifications such as acetylation, methylation, and phosphorylation of the histone tails, represents a fundamental regulatory mechanism of gene expression/repression (5Strahl B.D. Allis C.D. Nature. 2000; 403: 41-45Crossref PubMed Scopus (6782) Google Scholar). Various hypotheses have suggested that a single modification or specific combinations of histone modifications may affect distinct downstream events by altering the chromatin structure and/or generating a binding platform for protein effectors that specifically recognize the modification(s) and initiate gene transcription or repression (5Strahl B.D. Allis C.D. Nature. 2000; 403: 41-45Crossref PubMed Scopus (6782) Google Scholar, 6Fischle W. Wang Y. Allis C.D. Curr. Opin. Cell Biol. 2003; 15: 172-183Crossref PubMed Scopus (1000) Google Scholar). Acetylation of the histone tails is one of the most thoroughly characterized features of chromatin remodeling and transcriptional activation (4Roth S.Y. Denu J.M. Allis C.D. Annu. Rev. Biochem. 2001; 70: 81-120Crossref PubMed Scopus (1660) Google Scholar, 7Brownell J.E. Allis C.D. Curr. Opin. Genet. Dev. 1996; 6: 176-184Crossref PubMed Scopus (477) Google Scholar). The acetylated N-terminal tails of the histones are recognized by the bromodomain, a conserved sequence motif composed of ∼110 amino acids (8Haynes S.R. Dollard C. Winston F. Beck S. Trowsdale J. Dawid I.B. Nucleic Acids Res. 1992; 20: 2603Crossref PubMed Scopus (332) Google Scholar, 9Zeng L. Zhou M.M. FEBS Lett. 2002; 513: 124-128Crossref PubMed Scopus (580) Google Scholar) that was originally identified in the Drosophila protein brahma (8Haynes S.R. Dollard C. Winston F. Beck S. Trowsdale J. Dawid I.B. Nucleic Acids Res. 1992; 20: 2603Crossref PubMed Scopus (332) Google Scholar, 10Tamkun J.W. Deuring R. Scott M.P. Kissinger M. Pattatucci A.M. Kaufman T.C. Kennison J.A. Cell. 1992; 68: 561-572Abstract Full Text PDF PubMed Scopus (798) Google Scholar). The specific recognition of acetylated lysine on the histone N-terminal tails by the bromodomain is considered to be a major characteristic of chromatin activation. The bromodomain is present in many chromatin-associated factors such as nuclear histone acetyltransferases, ATP-dependent chromatin remodeling factors, and the BET family of nuclear proteins. Recent evidence has shown that the development of human cancers by transcriptional dysfunction is caused by genetic alterations of these bromodomain genes (11Lavau C. Du C. Thirman M. Zeleznik-Le N. EMBO J. 2000; 19: 4655-4664Crossref PubMed Scopus (172) Google Scholar, 12French C.A. Miyoshi I. Aster J.C. Kubonishi I. Kroll T.G. Dal Cin P. Vargas S.O. Perez-Atayde A.R. Fletcher J.A. Am. J. Pathol. 2001; 159: 1987-1992Abstract Full Text Full Text PDF PubMed Scopus (161) Google Scholar, 13Liedman D. Zeleznik-Le N. Curr. Opin. Hematol. 2001; 8: 218-223Crossref PubMed Scopus (10) Google Scholar, 14Ohshima T. Suganuma T. Ikeda M. Biochem. Biophys. Res. Commun. 2001; 281: 569-575Crossref PubMed Scopus (28) Google Scholar, 15Panagopoulos I. Fioretos T. Isaksson M. Samuelsson U. Billstrom R. Strombeck B. Mitelman F. Johansson B. Hum. Mol. Genet. 2001; 10: 395-404Crossref PubMed Scopus (181) Google Scholar). The proteins belonging to the BET family have a unique feature in that they contain two tandem bromodomains and an additional conserved ET domain (16Thorpe K.L. Abdulla S. Kaufman J. Trowsdale J. Beck S. Immunogenetics. 1996; 44: 391-396Crossref PubMed Scopus (36) Google Scholar). In vertebrates, four members of the BET family have been identified: BRD2/RING3/FSRG1 (16Thorpe K.L. Abdulla S. Kaufman J. Trowsdale J. Beck S. Immunogenetics. 1996; 44: 391-396Crossref PubMed Scopus (36) Google Scholar, 17Beck S. Hanson I. Kelly A. Pappin D.J. Trowsdale J. DNA Sequence. 1992; 2: 203-210Crossref PubMed Scopus (80) Google Scholar), BRD3/ORFX/FSRG2 (18Thorpe K.L. Gorman P. Thomas C. Sheer D. Trowsdale J. Beck S. Gene (Amst.). 1997; 200: 177-183Crossref PubMed Scopus (31) Google Scholar), BRD4/HUNK1/MCAP (mitotic chromosome-associated protein) (19Dey A. Ellenberg J. Farina A. Coleman A.E. Maruyama T. Sciortino S. Lippincott-Schwartz J. Ozato K. Mol. Cell. Biol. 2000; 20: 6537-6549Crossref PubMed Scopus (241) Google Scholar), and BRD5/BRDT (20Jones M.H. Numata M. Shimane M. Genomics. 1997; 45: 529-534Crossref PubMed Scopus (91) Google Scholar). BRD2/RING3/fsrg1 was initially identified as a novel gene involved in the regulation of the human major histocompatibility complex class II region and was initially named RING3 (really interesting new gene-3) (17Beck S. Hanson I. Kelly A. Pappin D.J. Trowsdale J. DNA Sequence. 1992; 2: 203-210Crossref PubMed Scopus (80) Google Scholar, 21Okamoto N. Ando A. Kawai J. Yoshiwara T. Tsuji K. Inoko H. Hum. Immunol. 1991; 32: 221-228Crossref PubMed Scopus (13) Google Scholar), but was subsequently renamed BRD2. BRD2 contains a kinase-like domain between the two bromodomains, consistent with the fact that it has mitogen-activated nuclear kinase activity and is involved in signal transduction (22Denis G.V. Green M.R. Genes Dev. 1996; 10: 261-271Crossref PubMed Scopus (118) Google Scholar). Through its bromodomains, BRD2 selectively interacts with the acetylated Lys12 of histone H4 in the intact nuclei of living cells and activates transcription from the cyclin E promoter (23Kanno T. Kanno Y. Siegel R.M. Jang M.K. Lenardo M.J. Ozato K. Mol. Cell. 2004; 13: 33-43Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar). Furthermore, BRD2 associates with acetylated chromatin during mitosis (19Dey A. Ellenberg J. Farina A. Coleman A.E. Maruyama T. Sciortino S. Lippincott-Schwartz J. Ozato K. Mol. Cell. Biol. 2000; 20: 6537-6549Crossref PubMed Scopus (241) Google Scholar, 23Kanno T. Kanno Y. Siegel R.M. Jang M.K. Lenardo M.J. Ozato K. Mol. Cell. 2004; 13: 33-43Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar, 24Dey A. Chitsaz F. Abbasi A. Misteli T. Ozato K. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 8758-8763Crossref PubMed Scopus (513) Google Scholar), whereas the other bromodomain family proteins are known to be displaced from the chromosomes during mitosis (25Martinez-Balbas M.A. Dey A. Rabindran S.K. Ozato K. Wu C. Cell. 1995; 83: 29-38Abstract Full Text PDF PubMed Scopus (377) Google Scholar, 26Muchardt C. Reyes J.C. Bourachot B. Leguoy E. Yaniv M. EMBO J. 1996; 15: 3394-3402Crossref PubMed Scopus (195) Google Scholar, 27Kruhlak M.J. Hendzel M.J. Fischle W. Bertos N.R. Hameed S. Yang X.J. Verdin E. Bazett-Jones D.P. J. Biol. Chem. 2001; 276: 38307-38319Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar). In addition, BRD4/MCAP, another member of the BET family, also associates with acetylated chromatin throughout the cell cycle (19Dey A. Ellenberg J. Farina A. Coleman A.E. Maruyama T. Sciortino S. Lippincott-Schwartz J. Ozato K. Mol. Cell. Biol. 2000; 20: 6537-6549Crossref PubMed Scopus (241) Google Scholar, 24Dey A. Chitsaz F. Abbasi A. Misteli T. Ozato K. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 8758-8763Crossref PubMed Scopus (513) Google Scholar) and helps viral DNA to remain attached to the host's mitotic chromosomes (28You J. Croyle J.L. Nishimura A. Ozato K. Howley P.M. Cell. 2004; 117: 349-360Abstract Full Text Full Text PDF PubMed Scopus (313) Google Scholar). Hence, the retention on chromosomes during mitosis is likely to be a distinctive feature of the BET family. The bromodomains within the BET family members probably play an important role in the epigenetic memory of transcription and viral inheritance across cell division. Nevertheless, it is still not clear 1) how BRD2 recognizes the specific acetylated histone code and 2) how BRD2 can associate with the acetylated chromatin for a prolonged time during cell division. To understand the molecular mechanism of the BRD2 bromodomain in more detail, we determined the crystal structure of the N-terminal bromodomain I (BD1 4The abbreviations used are: BD1, bromodomain I; MES, 4-morpholineethanesulfonic acid; DTT, dithiothreitol; TEV, tobacco etch virus; NCS, non-crystallographic symmetry; GFP, green fluorescent protein; SPR, surface plasmon resonance; CBP, cAMP-responsive element-binding proteinbinding protein; PCAF, p300/CBP-associated factor; BD2, bromodomain II. ; residues 74-194) of human BRD2. Intriguingly, BRD2 BD1 forms an intact homodimer in both crystals and solution. In addition to the two acetyllysine-binding pockets, the dimer interface makes a potential acidic cleft, suggesting that this secondary binding pocket, together with the acetyllysine-binding pockets, may play a crucial role in BRD2 BD1 recognition of a specific acetylated histone H4 tail. Construction of BRD2 BD1 Expression BD1 74-194) of human BRD2 R.D. L. B. Natl. Acad. Sci. U. S. A. 2002; PubMed Scopus Google Scholar) was by the and This was by to the promoter and a sequence within the and the sequence within the T. T. Y. M. Y. T. S. FEBS Lett. 1999; PubMed Scopus Google Scholar). This was the for protein Expression and of BRD2 of human BRD2 was produced as a protein with an N-terminal and a The protein was produced by the T. T. Y. M. Y. T. S. FEBS Lett. 1999; PubMed Scopus Google Scholar). The protein was first to a in and and with and The was by with the at for To the and the from the the was to a The was and a with The protein was by a of The and to a with and The protein was to the by of protein in and with of and the of at the and single crystals for the protein within in a and The of the crystals used for was The crystals in a and in to the of for the crystal was at at the an The was to The was with between two The and with the W. 1997; 276: PubMed Scopus Google Scholar). The crystal to the with cell of a and and the of in the the and are and are in of and to in are the in the and to protein was with of the from The in are the in the and was with of the from in a new and structure was with both the and the T.C. J. Biol. 1999; PubMed Scopus Google Scholar). the produced with the the in the an of of for to The by with non-crystallographic and to the T.C. Biol. 2000; PubMed Scopus Google Scholar). The by was and of the protein The of the protein the M. Biol. 1991; PubMed Scopus Google Scholar). of by and with between the in the an of and The was with P. J. M. T. Biol. PubMed Scopus Google Scholar) a that and used throughout the to and to the of between the the The at of residues and one MES, one DTT, and with a of and for residues and in and In addition, the for residues at the N-terminal of was also The of the protein is as with R. J.M. J. Google Scholar). The for this structure are in at a and a with two protein and in and was used in the and with the two protein The a of a of and a molecular of and BRD2 (23Kanno T. Kanno Y. Siegel R.M. Jang M.K. Lenardo M.J. Ozato K. Mol. Cell. 2004; 13: 33-43Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar) and cells with the or green fluorescent protein and for The of DNA was by or The nuclear was in DTT, and at for and DTT, and The nuclear from cells with the was with for at and with protein with on and to H4 BD1 74-194) of human BRD2 R.D. L. B. Natl. Acad. Sci. U. S. A. 2002; PubMed Scopus Google Scholar) was the of BRD2 BD1 was in the BD1 of the residues within the dimer interface of BRD2 BD1 the by the II BRD2 BD1 and and in E. and by on a and a The of the proteins was by histone H4 acetylated at Lys12 to the N-terminal region of histone was by and from The was on the surface of a and the binding of the and BRD2 BD1 proteins by surface plasmon on a with as the The was in for each BRD2 BD1 and The binding was as from the cell with H4 from the of BRD2 structure of BD1 of BRD2 74-194) was by the at and to 1) with The structure contains a by four and The structure of BD1 of BRD2 is to of the bromodomains of p300/CBP-associated factor C. J.E. L. C. Zhou M.M. Nature. 1999; PubMed Scopus Google Scholar), human M.A. J. Mol. Biol. 2000; PubMed Scopus Google Scholar), D.J. P. Yang J.C. N. P. D. P. EMBO J. 2000; 19: PubMed Scopus Google Scholar), S. Y. L. A. J.E. M. Verdin E. Zhou M.M. Mol. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar), and S. Y. L. S. Zeleznik-Le Zhou M.M. Mol. Cell. 2004; 13: Full Text Full Text PDF PubMed Scopus Google Scholar) and the of R. 2000; PubMed Scopus Google Scholar). The binding within BD1 is defined by an that and and by another that and two a cleft, with a in the of the The hydrophobic core of the domain is by the conserved hydrophobic residues and by conserved The BD1 sequence to the structure residues of BRD2, with tail at the N- and C-terminal regions of BRD2 crystal contains in the The of the are in the regions as from the of by of the Intriguingly, the of the is unique with in other protein is by whereas is by a of to B. forms a dimer with a by in a to the of and and the is in the regions of the and and In the other of formation between and the N- and C-terminal tail regions of have with the residues within the region of C. The surface potential that the dimer interface of and is hydrophobic The potential is by a of charged residues on the central of and of the the that the buried surface of a in the dimer is which to of the surface of a the buried surface in the dimer is In for the the is to of the The of and are for with molecular J.M. Curr. Opin. Biol. 1996; 6: PubMed Scopus Google Scholar). the and dimers are likely to be The of BD1 in the crystal is consistent with the from in and in The of the are in the regions as from the of by of the of BD1 in and in structure of BD1 in was by two a of the from the a molecular of that BRD2 BD1 molecular of as a dimer in of BRD2 BD1 with a consistent with the of BD1 that BRD2 BD1 as a in To the BRD2 protein interacts with another BRD2 in we a with nuclear from cells and with in cells both proteins, but not in cells the or a single that the BRD2 protein interacts with another BRD2 in To the of the in we shown in BD1 BRD2 To the residues responsible for the of BRD2, we BRD2 BD1 proteins with of the residues to the and their to with BRD2. BRD2 BD1 and the to with BRD2 in The and with BRD2 that the residues within the BRD2 BD1 dimer which identified by the are involved in the of BRD2 in of BRD2 BD1 in the H4 the BRD2 BD1 proteins an intact we additional binding studies to the the of the histone H4 acetylated at Lys12. was with an H4 to the N-terminal region and acetylated at Lys12 BRD2 shown in BRD2 BD1 to the consistent with (23Kanno T. Kanno Y. Siegel R.M. Jang M.K. Lenardo M.J. Ozato K. Mol. Cell. 2004; 13: 33-43Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar). with the BRD2 BD1 and which are in the dimer interface the that the binding of BRD2 BD1 for the was by the In this we determined the structure of the N-terminal bromodomain of BRD2, which to the BET family. the molecular mechanism of histone tail recognition by BD1 of BRD2 as a that BRD2 specifically recognizes acetylated histone H4 through Lys12 (23Kanno T. Kanno Y. Siegel R.M. Jang M.K. Lenardo M.J. Ozato K. Mol. Cell. 2004; 13: 33-43Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar) and also demonstrated that one intact BRD2 bromodomain is for a with histone H4 acetylated at Lys12 by binding and in living of the BD1 and bromodomain II in the BRD2 and proteins that the bromodomains in BRD2 and BRD2 BD1 BD1 and BRD2 BD2, are with the bromodomains, BD1 The bromodomains sequence whereas sequence between BD1 and among other BET proteins also not The of the BRD2 BD1 residues that to the dimer interface are conserved between BRD2 BD1 and BD1 This that BD1 of may also the to a as in the BRD2 BD1 In the of BD2, the residues within the dimer interface are not conserved with their residues in BD1 of the of the with the sequence to BD1, it is likely that the of the be in the regions of BET proteins with that in additional of be to this of the structure of BRD2 BD1 with the known histone bromodomain of human M.A. J. Mol. Biol. 2000; PubMed Scopus Google Scholar), D.J. P. Yang J.C. N. P. D. P. EMBO J. 2000; 19: PubMed Scopus Google Scholar), human S. Y. L. A. J.E. M. Verdin E. Zhou M.M. Mol. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar), and human S. Y. L. S. Zeleznik-Le Zhou M.M. Mol. Cell. 2004; 13: Full Text Full Text PDF PubMed Scopus Google Scholar) and the of R. 2000; PubMed Scopus Google Scholar) that the of BRD2 BD1 has been conserved among the bromodomain family proteins C. J.E. L. C. Zhou M.M. Nature. 1999; PubMed Scopus Google Scholar). the of these bromodomains are major in the and regions sequence of is among these The complex structure of the bromodomain with the histone H4 acetylated at that this bromodomain to an at D.J. P. Yang J.C. N. P. D. P. EMBO J. 2000; 19: PubMed Scopus Google Scholar). a was four residues to the and a of with the the and sequence in the and regions between the bromodomain and BRD2 BD1, we that BRD2 BD1 may recognize the H4 tail in a additional of the BRD2 BD1 complex with the are to understand how the BRD2 BD1 protein recognizes the acetylated H4 tail. The complex not to DNA 1996; PubMed Scopus Google Scholar, C. M. Mol. Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar), and the is by transcription factor S. II, Mol. Cell. 1999; Full Text Full Text PDF PubMed Scopus (36) Google Scholar). the of transcription factor which contains the bromodomain, a complex with four The structure of the bromodomain R. 2000; PubMed Scopus Google Scholar) is from that of the BRD2 BD1 homodimer In the of the the is by between and the region of BD1 and between and the region of BD2, and the of a R. 2000; PubMed Scopus Google Scholar). the other in the of the BRD2 BD1 the between and of BRD2 BD1 is in the regions of and and the and the structure has a non-crystallographic and we for a between the and the histone tail to the N-terminal tail of histone H4 at or also to the N-terminal tail of histone acetylated at the other the BET family proteins BRD2 and specifically recognize the histone H4 N-terminal tail acetylated at as by studies (23Kanno T. Kanno Y. Siegel R.M. Jang M.K. Lenardo M.J. Ozato K. Mol. Cell. 2004; 13: 33-43Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar, 24Dey A. Chitsaz F. Abbasi A. Misteli T. Ozato K. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 8758-8763Crossref PubMed Scopus (513) Google Scholar). that BRD2 and have a more specific recognition mechanism for the acetylated histone tail with we that the specific recognition of a acetylated of the histone H4 tail by BRD2 BD1 be by the surface potential of the BRD2 BD1 In the present we demonstrated that of the residues within the BRD2 BD1 dimer interface the binding of this protein for the also that and in the binding to with BRD2 BD1 that the dimer formation is for the of BRD2 BD1 with the tail. Intriguingly, the surface potential of the BRD2 BD1 homodimer a negatively charged which is in the bromodomain not in addition to the two hydrophobic pockets that recognize acetylated The acidic which at the dimer is by the of and thus that this negatively charged be a potential secondary binding for with a basic of the acetylated histone H4 tail. the histone H4 N-terminal tail is basic and as and are the acetylated Lys12 it is that or interacts with BRD2 BD1 through this secondary binding as this and (23Kanno T. Kanno Y. Siegel R.M. Jang M.K. Lenardo M.J. Ozato K. Mol. Cell. 2004; 13: 33-43Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar, 24Dey A. Chitsaz F. Abbasi A. Misteli T. Ozato K. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 8758-8763Crossref PubMed Scopus (513) Google Scholar) studies also the BRD2 BD1 recognition of the Lys12 of the H4 the present structure that the BRD2 BD1 homodimer may recognize two acetylated H4 tails additional of BRD2 BD1 with the acetylated H4 tail are to understand the molecular mechanism of BRD2 BD1 recognition of the acetylated H4 tail. In BRD2 BD1 forms a homodimer in the crystal as well as in solution. The acidic at the dimer interface and the two acetyllysine-binding in the BRD2 BD1 protein how the N-terminal bromodomain of the BET family proteins recognizes the histone code by of the acetylated histone H4 tail. a for and studies at how the BET family proteins with acetylated nucleosomes and the transcriptional in a histone the of for in also E. C. Y. and T. for are to T. K. and A. for with