Readout of chromatin marks by histone-binding modules
Haitao Li*, Sean D. Taverna*, Alexander J. Ruthenburg*, Dinshaw J. Patel & C. David Allis
Combinations of histone posttranslational modifications and DNA methylation appear to regulate thephysical properties of the chromatin fibre, either directly or via specific protein adaptors termed‘effectors’. Recent studies have shown that these effector modules bind to histone tails in amodification state-specific manner. Emerging hints that many putative effector modules coexist within
the same protein complex suggest that multivalent engagement of chromatin substrates may be afunctionally important phenomenon.

Eukaryotic genomes are presented to cellular factors in the form of chromatin, wherein a nucleosome
serves as the fundamental subunit, which consists of DNA wrapped around a core of histone proteins.
Access to genetic information is controlled in part by the posttranslational modification of histones
and 5-methylcytosine methylation of DNA. Distinct sets of these chromatin marks are associated withmost DNA transactions and have been implicated as carriers of epigenetic identity, although precise
mechanisms connecting the marks to functional consequences are only beginning to emerge.

Marks, modules and multivalency
Histones can be covalently modified by the addition of a variety ofchemical appendages that create binding sites for specific protein
modules. The top panel illustrates the chemical structures of the small
modifications that have been most intensively studied. Many
examples of histone-binding, or effector, modules are known; shownin the middle panel are representative examples of each different
class of protein fold (grey) in complex with its cognate modified
histone-binding partner (yellow); see also Table 1.
In most cases, residues that line the binding pocket (red) of amodule dictate the modification state of a mark that is preferentiallybound, while residues outside the binding pocket contribute to muchof the histone sequence specificity. In several instances, similar folds
bind different marks: for example, tudor domains can bind Kme3
(JMJD2A) or Kme2 (53BP1), and PHD fingers can bind exclusively
Kme2/3 (BPTF) or unmodified K (BHC80). The structural
underpinnings of this methyl-state specific readout (K, Kme1, Kme2or Kme3) are demonstrated by comparing the four different
structures displayed in the ‘Different methyl state recognition’ panel.
In many cases, there is no longer a clear correlation between asingle histone mark and its function. For example, the Kme3 mark,when in the context of the N terminus of H3 (K4me3), can be boundby PHD fingers of proteins in complexes that either activate (forexample, the BPTF subunit of the NURF complex in homeotic gene
remodelling enhances transcription) or repress gene expression (forexample, the ING2 subunit of the Sin3a–HDAC complex is involved in
repression following DNA damage). Analyses of native histone
modification states has increased our appreciation that histone PTMs
occur in various combinations rather than in isolation (see Table 2),
which may help account for this paradox. Perhaps multivalentinteractions with discrete patterns dictate composite specificity andenhance the affinity of chromatin-associated complexes.

Histone marks++Different methyl state recognition+++++

PHD finger (BHC80)

MBT (L3MBTL1)

–K

Kme1

Kme2

Kme3

Kac

Cit

R

Rme1

Rme2s

Rme2a

Yph

K

Tph

Kme1Histone-binding modules
Kac

Kme2

Kme3

K
Kme2
PHD finger (BHC80)

Kme3

Themes of recognition

R
Kme3
Tudor (53BP1)

Free
N-terminus
interactions

Bromo (Gcn5)

Kme3

WD40r (WDR5)

N+2 or N–2
residuerecognition

Aromatic cage

PHD finger (ING2)
Sph
Kme2

Kme3

MBT (L3MBTL1)

Tudor (JMJD2A)

Induced β-strand forhistone peptide

tandem BRCT (MDC1)

14-3-3 (14-3-3ζ)Tudor

H3K4me2/3, H3K9me2/3,
H3K27me2/3
H3K4me3, H4K20me2

MBT
WD40 repeats
Bromodomain
PHD
14-3-3BRCT

H3K4me1, H4K20me1/2, H1K26me1
R2/H3K4me2?
Kac
H3K4, H3K4me3, H3K9me3, K36me3
H3S10phH2A.XS139phIntranucleosomal
Oligovalent complex

BAH2BPTF

H44

H3

H4H36

PWWP

H47SANT
H3

H3

Trans-histone

HP1
Adjacent bridging

Histones and Transcription at Abcam
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Transcriptionally active chromatin
Mitogen-stimulated transcription

H3R17me1/me2a + H3K18ac Oestrogen-stimulated transcription
Chaperone association
H4K5ac + H4K12ac
Pre-deposition
Stem cell transcriptional plasticity
H3K4me3 + H3K27me3‘Bivalent domains’ at key
developmental genes
Transcriptional repression
H3K9me3 + H3K27me3
Silent loci+ CpG 5-MeC
H3K27me3 + H2AK119ub1 Silent homeotic genes
Heterochromatin
H3K9me3 + H4K20me3+ CpG 5-MeC
H3K9me2/3 + H4K20me1
Inactive X-chromosome+ H4K27me3 + CpG 5-MeC

Contact information:Bromo

PHD

HP1

H3K4me2/3 +H3K9/14/18/23ac
H3S10ph + H3K14ac

Transcriptionally active homeoticgenes

34H3

Locus/chromatin state

WD40r

Static effectormodule pockets

Internucleosomal

Oligovalent protein

Histone marks
Transcriptional activation
H3K4me2/3 + H4K16ac

53BP1, p53 binding protein-1; 5-MeC, 5-methylcytosine;
BAH, bromo-adjacent homology domain; BHC80, BRAF-HDACcontaining protein; BPTF, bromodomain PHD finger transcription
factor; BRCT, breast cancer carboxy-terminal domain;
Bromo, bromodomain; Chromo, chromodomain; Cit, citrulline;
CpG, the DNA sequence that is often targeted for epigenetic
5-cytosine methylation; Double chromo, double chromodomain;
HP1, heterochromatin protein 1; ING2, inhibitor of growthprotein-2; JMJD2A, jumonji domain-containing protein 2A;K, lysine; Kac, acetylated lysine; Kme1, mono-methylated lysine;Kme2, di-methylated lysine; Kme3 tri-methylated lysine;
MBT, malignant brain tumour; PHD finger, plant homeodomain
finger; PTM, posttranslational modification; R, arginine;Rme1, mono-methylated arginine; Rme2a, asymmetric dimethylated arginine; Rme2s, symmetric di-methylated arginine;Sph, phosphorylated serine; Tph, phosphorylated threonine;Yph, phosphorylated tyrosine; WD40r, WD40 repeat.

Module connectivity

Modes of multivalent chromatin engagement

Cis-histone

Known histone marks

Abbreviations

SphDouble chromo (CHD1)

hTaf1

Histone-binding or
effector module
Chromodomain

Table 2 | Functional associations of coexisting marks

Royal family

Chromo (HP1)

Table 1 | Recognition of histone marks by modules

PHD finger (BPTF)

Tudor (53BP1)

Modes of multivalent chromatin engagement
Histone-binding modules are often found in the same protein withother binding modules, suggesting a means to simultaneously interact
with particular combinations of modifications and a mechanism forincreasing the affinity of complexes for chromatin (lower panel). The
number of proteins with multiple potential histone-binding modules in
the human proteome (http://smart.embl-heidelberg.de) are shown
schematically in the ‘Module connectivity’ panel. We would like toarticulate nomenclature to describe the possible modes ofmultivalent recognition, as distinguishing among these permutations
is important for future studies.
Intranucleosomal: mechanisms for simultaneous histone-tail binding
in the same nucleosome.
• Cis-histone: Tandem modules bind to marks that are present on thesame histone tail.
• Trans-histone: Modules in a protein or complex bind to marks thatare present on different histone tails.
Internucleosomal: mechanisms for simultaneous histone-tail binding
in different nucleosomes.
• Adjacent bridging: Multiple modules engage marks on adjacentnucleosomes.
• Discontinuous bridging: Multiple modules engage marks on
nonadjacent nucleosomes.

–+Sph

Themes of recognition
Emerging themes in the molecular recognition of modified histones
are illustrated in the context of the PHD finger of BPTF, and appear tobe the product of convergent evolution.
• The histone peptide often engages the binding module in an induced
β-strand backbone conformation, whereas the protein-binding
modules remain relatively static.
• Aromatic residues in the module envelop histone methylation in acation-π cage as also depicted in the ‘Different methyl state
recognition’ panel.
• Residues in the N+2 or N-2 position with respect to the histone markare often crucial determinants of binding sequence specificity.
• Additional specificity may be imparted by recognition of a free N
terminus.

–Linked review article:
Ruthenburg, A.J., Li, H., Taverna, S.D., Patel, D.J. & Allis, C.D. Multivalentengagement of chromatin modifications by linked binding modules.
Nature Rev. Mol. Cell Biol. 8, xx–xx (2007).

Further reading:Bernstein, B.E. et al. A bivalent chromatin structure marks key
developmental genes in embryonic stem cells. Cell 125, 315–326 (2006).
Cheng, X., Collins, R.E. & Zhang, X. Structural and sequence motifs ofprotein (histone) methylation enzymes. Annu. Rev. Biophys. Biomol.
Struct. 34, 267–294 (2005).

S. D. Taverna, A. J. Ruthenburg, and C. D. Allis are at the Laboratoryof Chromatin Biology and Epigenetics, The Rockefeller University,
1230 York Ave, Room 1501, New York, NY, 10065, USA. | C. D. Allis’
homepage: www.rockefeller.edu/labheads/allis/index.php | H. Liand D. J. Patel are at the Structural Biology Program, Memorial
Sloan-Kettering Cancer Center, New York, NY, 10021, USA. | D. J.
Patel’s homepage: www.mskcc.org/mskcc/html/10829.cfm*Authors contributed equally to this work.
Poster design by Vicky Askew. Edited by Arianne Heinrichs.
© 2007 Nature Publishing Group.
www.nature.com/nrm/poster/xxx

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