Linker histones as liquid-like glue for chromatin

Linker histone H1 drives heterochromatin condensation via phase separation in Arabidopsis

In the eukaryotic nucleus, heterochromatin forms highly condensed, visible foci known as heterochromatin foci (HF). These HF are enriched with linker histone H1, a key player in heterochromatin condensation and silencing. However, it is unknown how H1 aggregates HF and condenses heterochromatin. In this study, we established that H1 facilitates heterochromatin condensation by enhancing inter- and intrachromosomal interactions between and within heterochromatic regions of the Arabidopsis (Arabidopsis thaliana) genome. We demonstrated that H1 drives HF formation via phase separation, which requires its C-terminal intrinsically disordered region (C-IDR). A truncated H1 lacking the C-IDR fails to form foci or recover HF in the h1 mutant background, whereas C-IDR with a short stretch of the globular domain (18 out of 71 amino acids) is sufficient to rescue both defects. In addition, C-IDR is essential for H1's roles in regulating nucleosome repeat length and DNA methylation in Arabidopsis, indicating that phase separation capability is required for chromatin functions of H1. Our data suggest that bacterial H1-like proteins, which have been shown to condense DNA, are intrinsically disordered and capable of mediating phase separation. Therefore, we propose that phase separation mediated by H1 or H1-like proteins may represent an ancient mechanism for condensing chromatin and DNA.

Extreme dynamics in a biomolecular condensate

Proteins and nucleic acids can phase-separate in the cell to form concentrated biomolecular condensates^1-4. The functions of condensates span many length scales: they modulate interactions and chemical reactions at the molecular scale⁵, organize biochemical processes at the mesoscale⁶ and compartmentalize cells⁴. Understanding the underlying mechanisms of these processes will require detailed knowledge of the rich dynamics across these scales⁷. The mesoscopic dynamics of biomolecular condensates have been extensively characterized⁸, but their behaviour at the molecular scale has remained more elusive. Here, as an example of biomolecular phase separation, we study complex coacervates of two highly and oppositely charged disordered human proteins⁹. Their dense phase is 1,000 times more concentrated than the dilute phase, and the resulting percolated interaction network¹⁰ leads to a bulk viscosity 300 times greater than that of water. However, single-molecule spectroscopy optimized for measurements within individual droplets reveals that at the molecular scale, the disordered proteins remain exceedingly dynamic, with their chain configurations interconverting on submicrosecond timescales. Massive all-atom molecular dynamics simulations reproduce the experimental observations and explain this apparent discrepancy: the underlying interactions between individual charged side chains are short-lived and exchange on a pico- to nanosecond timescale. Our results indicate that, despite the high macroscopic viscosity of phase-separated systems, local biomolecular rearrangements required for efficient reactions at the molecular scale can remain rapid.

A novel molecular reporter for probing protein DNA recognition: An optical spectroscopic and molecular modeling study

A novel benzo[a]phenoxazine-based fluorescent dye LV2 has been employed as a molecular reporter to probe recognition of a linker histone protein H1 by calf-thymus DNA (DNA). Fluorescence lifetime of LV2 buried in the globular domain of H1 (∼2.1 ns) or in the minor groove of DNA (∼0.93 ns) increases significantly to 2.65 ns upon interaction of the cationic protein with DNA indicating formation of the H1-DNA complex. The rotational relaxation time of the fluorophore buried in the globular domain of H1 increases significantly from 2.2 ns to 8.54 ns in the presence of DNA manifesting the recognition of H1 by DNA leading to formation of the H1-DNA complex. Molecular docking and molecular dynamics (MD) simulations have shown that binding of LV2 is energetically most favourable in the interface of the H1-DNA complex than in the globular domain of H1 or in the minor groove of DNA. As a consequence, orientational relaxation of the LV2 is significantly hindered in the protein-DNA interface compared to H1 or DNA giving rise to a much longer rotational relaxation time (8.54 ns) in the H1-DNA complex relative to that in pure H1 (2.2 ns) or DNA (5.7 ns). Thus, via a significant change of fluorescence lifetime and rotational relaxation time, the benzo[a]phenoxazine-based fluorescent dye buried within the globular domain of the cationic protein, or within the minor groove of DNA, reports on recognition of H1 by DNA.

Loss of H3K9 trimethylation alters chromosome compaction and transcription factor retention during mitosis

Recent studies have shown that repressive chromatin machinery, including DNA methyltransferases and polycomb repressor complexes, binds to chromosomes throughout mitosis and their depletion results in increased chromosome size. In the present study, we show that enzymes that catalyze H3K9 methylation, such as Suv39h1, Suv39h2, G9a and Glp, are also retained on mitotic chromosomes. Surprisingly, however, mutants lacking histone 3 lysine 9 trimethylation (H3K9me3) have unusually small and compact mitotic chromosomes associated with increased histone H3 phospho Ser10 (H3S10ph) and H3K27me3 levels. Chromosome size and centromere compaction in these mutants were rescued by providing exogenous first protein lysine methyltransferase Suv39h1 or inhibiting Ezh2 activity. Quantitative proteomic comparisons of native mitotic chromosomes isolated from wild-type versus Suv39h1/Suv39h2 double-null mouse embryonic stem cells revealed that H3K9me3 was essential for the efficient retention of bookmarking factors such as Esrrb. These results highlight an unexpected role for repressive heterochromatin domains in preserving transcription factor binding through mitosis and underscore the importance of H3K9me3 for sustaining chromosome architecture and epigenetic memory during cell division.

Epithelial cells-enriched lncRNA SNHG8 regulates chromatin condensation by binding to Histone H1s

Linker histone H1 proteins contain many variants in mammalian and can stabilize the condensed state of chromatin by binding to nucleosomes and promoting a more inaccessible structure of DNA. However, it is poorly understood how the binding of histone H1s to chromatin DNA is regulated. Screened as one of a collection of epithelial cells-enriched long non-coding RNAs (lncRNAs), here we found that small nucleolar RNA host gene 8 (SNHG8) is a chromatin-localized lncRNA and presents strong interaction and phase separation with histone H1 variants. Moreover, SNHG8 presents stronger ability to bind H1s than linker DNA, and outcompetes linker DNA for H1 binding. Consequently, loss of SNHG8 increases the amount of H1s that bind to chromatin, promotes chromatin condensation, and induces an epithelial differentiation-associated gene expression pattern. Collectively, our results propose that the highly abundant SNHG8 in epithelial cells keeps histone H1 variants out of nucleosome and its loss contributes to epithelial cell differentiation.

Disordered regions tune order in chromatin organization and function

Intrinsically disordered proteins or hybrid proteins with ordered domains and disordered regions (both collectively designated as IDP(R)s) defy the well-established structure-function paradigm due to their ability to perform multiple biological functions even in the absence of a well-defined 3D structure. IDP(R)s have a unique ability to exist as a functional heterogeneous ensemble, where they adopt multiple thermodynamically stable conformations with low energy barriers between states. The resultant structural plasticity or conformational adaptability provides them with a high functional diversity and ease of regulation. Hence, IDP(R)s are highly efficient biological machinery to mediate intricate cellular functions such as signaling, gene expression, and assembly of complex structures. One such structure is the nucleoprotein complex known as Chromatin. Interestingly, the proteins involved in shaping up the structure and function of chromatin are abundant in disordered regions, which serve more than just as mere flexible linkers. The disordered regions are involved in crucial processes such as gene expression regulation, chromatin architecture maintenance, and liquid-liquid phase separation initiation. This review is an attempt to explore the advantages and the functional and regulatory roles of intrinsic disorder in several Chromatin Associated Proteins from a mechanistic standpoint.

Release of linker histone from the nucleosome driven by polyelectrolyte competition with a disordered protein

Highly charged intrinsically disordered proteins are essential regulators of chromatin structure and transcriptional activity. Here we identify a surprising mechanism of molecular competition that relies on the pronounced dynamical disorder present in these polyelectrolytes and their complexes. The highly positively charged human linker histone H1.0 (H1) binds to nucleosomes with ultrahigh affinity, implying residence times incompatible with efficient biological regulation. However, we show that the disordered regions of H1 retain their large-amplitude dynamics when bound to the nucleosome, which enables the highly negatively charged and disordered histone chaperone prothymosin α to efficiently invade the H1-nucleosome complex and displace H1 via a competitive substitution mechanism, vastly accelerating H1 dissociation. By integrating experiments and simulations, we establish a molecular model that rationalizes the remarkable kinetics of this process structurally and dynamically. Given the abundance of polyelectrolyte sequences in the nuclear proteome, this mechanism is likely to be widespread in cellular regulation.

Chromatin-contact atlas reveals disorder-mediated protein interactions and moonlighting chromatin-associated RBPs

RNA-binding proteins (RBPs) play diverse roles in regulating co-transcriptional RNA-processing and chromatin functions, but our knowledge of the repertoire of chromatin-associated RBPs (caRBPs) and their interactions with chromatin remains limited. Here, we developed SPACE (Silica Particle Assisted Chromatin Enrichment) to isolate global and regional chromatin components with high specificity and sensitivity, and SPACEmap to identify the chromatin-contact regions in proteins. Applied to mouse embryonic stem cells, SPACE identified 1459 chromatin-associated proteins, ∼48% of which are annotated as RBPs, indicating their dual roles in chromatin and RNA-binding. Additionally, SPACEmap stringently verified chromatin-binding of 403 RBPs and identified their chromatin-contact regions. Notably, SPACEmap showed that about 40% of the caRBPs bind chromatin by intrinsically disordered regions (IDRs). Studying SPACE and total proteome dynamics from mES cells grown in 2iL and serum medium indicates significant correlation (R = 0.62). One of the most dynamic caRBPs is Dazl, which we find co-localized with PRC2 at transcription start sites of genes that are distinct from Dazl mRNA binding. Dazl and other PRC2-colocalised caRBPs are rich in intrinsically disordered regions (IDRs), which could contribute to the formation and regulation of phase-separated PRC condensates. Together, our approach provides an unprecedented insight into IDR-mediated interactions and caRBPs with moonlighting functions in native chromatin.

Structural features of nucleosomes in interphase and metaphase chromosomes

Structural heterogeneity of nucleosomes in functional chromosomes is unknown. Here, we devise the template-, reference- and selection-free (TRSF) cryo-EM pipeline to simultaneously reconstruct cryo-EM structures of protein complexes from interphase or metaphase chromosomes. The reconstructed interphase and metaphase nucleosome structures are on average indistinguishable from canonical nucleosome structures, despite DNA sequence heterogeneity, cell-cycle-specific posttranslational modifications, and interacting proteins. Nucleosome structures determined by a decoy-classifying method and structure variability analyses reveal the nucleosome structural variations in linker DNA, histone tails, and nucleosome core particle configurations, suggesting that the opening of linker DNA, which is correlated with H2A C-terminal tail positioning, is suppressed in chromosomes. High-resolution (3.4-3.5 Å) nucleosome structures indicate DNA-sequence-independent stabilization of superhelical locations ±0-1 and ±3.5-4.5. The linker histone H1.8 preferentially binds to metaphase chromatin, from which chromatosome cryo-EM structures with H1.8 at the on-dyad position are reconstituted. This study presents the structural characteristics of nucleosomes in chromosomes.

Protein intrinsic disorder on a dynamic nucleosomal landscape

The complex nucleoprotein landscape of the eukaryotic cell nucleus is rich in dynamic proteins that lack a stable three-dimensional structure. Many of these intrinsically disordered proteins operate directly on the first fundamental level of genome compaction: the nucleosome. Here we give an overview of how disordered interactions with and within nucleosomes shape the dynamics, architecture, and epigenetic regulation of the genetic material, controlling cellular transcription patterns. We highlight experimental and computational challenges in the study of protein disorder and illustrate how integrative approaches are increasingly unveiling the fine details of nuclear interaction networks. We finally dissect sequence properties encoded in disordered regions and assess common features of disordered nucleosome-binding proteins. As drivers of many critical biological processes, disordered proteins are integral to a comprehensive molecular view of the dynamic nuclear milieu.

Liquid-like chromatin in the cell: What can we learn from imaging and computational modeling?

Chromatin in eukaryotic cells is a negatively charged long polymer consisting of DNA, histones, and various associated proteins. With its highly charged and heterogeneous nature, chromatin structure varies greatly depending on various factors (e.g. chemical modifications and protein enrichment) and the surrounding environment (e.g. cations): from a 10-nm fiber, a folded 30-nm fiber, to chromatin condensates/droplets. Recent advanced imaging has observed that chromatin exhibits a dynamic liquid-like behavior and undergoes structural variations within the cell. Current computational modeling has made it possible to reconstruct the liquid-like chromatin in the cell by dealing with a number of nucleosomes on multiscale levels and has become a powerful technique to inspect the molecular mechanisms giving rise to the observed behavior, which imaging methods cannot do on their own. Based on new findings from both imaging and modeling studies, we discuss the dynamic aspect of chromatin in living cells and its functional relevance.

Extended and dynamic linker histone-DNA Interactions control chromatosome compaction

Chromatosomes play a fundamental role in chromatin regulation, but a detailed understanding of their structure is lacking, partially due to their complex dynamics. Using single-molecule DNA unzipping with optical tweezers, we reveal that linker histone interactions with DNA are remarkably extended, with the C-terminal domain binding both DNA linkers as far as approximately ±140 bp from the dyad. In addition to a symmetrical compaction of the nucleosome core governed by globular domain contacts at the dyad, the C-terminal domain compacts the nucleosome's entry and exit. These interactions are dynamic, exhibit rapid binding and dissociation, are sensitive to phosphorylation of a specific residue, and are crucial to determining the symmetry of the chromatosome's core. Extensive unzipping of the linker DNA, which mimics its invasion by motor proteins, shifts H1 into an asymmetric, off-dyad configuration and triggers nucleosome decompaction, highlighting the plasticity of the chromatosome structure and its potential regulatory role.

Binding Dynamics of Disordered Linker Histone H1 with a Nucleosomal Particle

Linker histone H1 is an essential regulatory protein for many critical biological processes, such as eukaryotic chromatin packaging and gene expression. Mis-regulation of H1s is commonly observed in tumor cells, where the balance between different H1 subtypes has been shown to alter the cancer phenotype. Consisting of a rigid globular domain and two highly charged terminal domains, H1 can bind to multiple sites on a nucleosomal particle to alter chromatin hierarchical condensation levels. In particular, the disordered H1 amino- and carboxyl-terminal domains (NTD/CTD) are believed to enhance this binding affinity, but their detailed dynamics and functions remain unclear. In this work, we used a coarse-grained computational model, AWSEM-DNA, to simulate the H1.0b-nucleosome complex, namely chromatosome. Our results demonstrate that H1 disordered domains restrict the dynamics and conformation of both globular H1 and linker DNA arms, resulting in a more compact and rigid chromatosome particle. Furthermore, we identified regions of H1 disordered domains that are tightly tethered to DNA near the entry-exit site. Overall, our study elucidates at near-atomic resolution the way the disordered linker histone H1 modulates nucleosome's structural preferences and conformational dynamics.

A variety-specific arrangement of histone H1 subtype (H1.b and H1.z) polymorphic variants in differently plumaged quails

1. This study was undertaken to evaluate genetic diversity among three varieties of Japanese quail (British Range, English White and Tuxedo) differing in plumage colour. The level of genetic variation was rated through the histone H1 polymorphic loci (H1.b and H1.z) containing quantitatively similar (P > 0.05) isoforms (H1.b1, H1.b2 and H1.z1, H1.z2) that form both homozygous (b1, b2 and z1, z2) and heterozygous (b1b2 and z1z2) phenotypes.2. The complete set of histone H1 phenotypes were characteristic of the British Range and Tuxedo varieties. Phenotypes b2 and z2 were not detected in the English White variety. A lack of the former phenotypes resulted in excess of heterozygotes at loci H1.b (F = -0.563) and H1.z (F = -0.562), pointing to the presence of outbreeding.3. The English White variety deviated from Hardy-Weinberg proportions (H1.b - Χ² = 7.61, P < 0.05 and H1.z - Χ² = 5.84, P < 0.05), in contrast to the British Range variety (H1.b - Χ² = 0.86, P > 0.05 and H1.z - Χ² = 0.86, P > 0.05) and Tuxedo (H1.b - Χ² = 1.6, P > 0.05 and H1.z - Χ² = 1.6, P > 0.05). The estimated values of the F_ST index for loci H1.b (0.073) and H1.z (0.099) indicate a moderate genetic diversity of the quail population.4. The distinct array and distribution of histone H1 phenotypes among quail varieties suggested that histone H1 allelic variants might have an individual impact on characteristic pigmentation of poultry.

Polyelectrolyte interactions enable rapid association and dissociation in high-affinity disordered protein complexes

Highly charged intrinsically disordered proteins can form complexes with very high affinity in which both binding partners fully retain their disorder and dynamics, exemplified by the positively charged linker histone H1.0 and its chaperone, the negatively charged prothymosin α. Their interaction exhibits another surprising feature: The association/dissociation kinetics switch from slow two-state-like exchange at low protein concentrations to fast exchange at higher, physiologically relevant concentrations. Here we show that this change in mechanism can be explained by the formation of transient ternary complexes favored at high protein concentrations that accelerate the exchange between bound and unbound populations by orders of magnitude. Molecular simulations show how the extreme disorder in such polyelectrolyte complexes facilitates (i) diffusion-limited binding, (ii) transient ternary complex formation, and (iii) fast exchange of monomers by competitive substitution, which together enable rapid kinetics. Biological polyelectrolytes thus have the potential to keep regulatory networks highly responsive even for interactions with extremely high affinities.

Linker histone H1.5 is an underestimated factor in differentiation and carcinogenesis

Human histone H1.5, in mice called H1b, belongs to the family of linker histones (H1), which are key players in chromatin organization. These proteins sit on top of nucleosomes, in part to stabilize them, and recruit core histone modifying enzymes. Through subtype-specific deposition patterns and numerous post-translational modifications, they fine-tune gene expression and chromatin architecture, and help to control cell fate and homeostasis. However, even though it is increasingly implicated in mammalian development, H1.5 has not received as much research attention as its relatives. Recent studies have focused on its prognostic value in cancer patients and its contribution to tumorigenesis through specific molecular mechanisms. However, many functions of H1.5 are still poorly understood. In this review, we will summarize what is currently known about H1.5 and its function in cell differentiation and carcinogenesis. We will suggest key experiments that are required to understand the molecular network, in which H1.5 is embedded. These experiments will advance our understanding of the epigenetic reprogramming occurring in developmental and carcinogenic processes.

Linker histone epitopes are hidden by in situ higher-order chromatin structure

BACKGROUND

Histone H1 is the most mobile histone in the cell nucleus. Defining the positions of H1 on chromatin in situ, therefore, represents a challenge. Immunoprecipitation of formaldehyde-fixed and sonicated chromatin, followed by DNA sequencing (xChIP-seq), is traditionally the method for mapping histones onto DNA elements. But since sonication fragmentation precedes ChIP, there is a consequent loss of information about chromatin higher-order structure. Here, we present a new method, xxChIP-seq, employing antibody binding to fixed intact in situ chromatin, followed by extensive washing, a second fixation, sonication and immunoprecipitation. The second fixation is intended to prevent the loss of specifically bound antibody during washing and subsequent sonication and to prevent antibody shifting to epitopes revealed by the sonication process. In many respects, xxChIP-seq is comparable to immunostaining microscopy, which also involves interaction of the primary antibody with fixed and permeabilized intact cells. The only epitopes displayed after immunostaining are the "exposed" epitopes, not "hidden" by the fixation of chromatin higher-order structure. Comparison of immunoprecipitated fragments between xChIP-seq versus xxChIP-seq should indicate which epitopes become inaccessible with fixation and identify their associated DNA elements.

RESULTS

We determined the genomic distribution of histone variants H1.2 and H1.5 in human myeloid leukemia cells HL-60/S4 and compared their epitope exposure by both xChIP-seq and xxChIP-seq, as well as high-resolution microscopy, illustrating the influences of preserved chromatin higher-order structure in situ. We found that xChIP and xxChIP H1 signals are in general negatively correlated, with differences being more pronounced near active regulatory regions. Among the intriguing observations, we find that transcription-related regions and histone PTMs (i.e., enhancers, promoters, CpG islands, H3K4me1, H3K4me3, H3K9ac, H3K27ac and H3K36me3) exhibit significant deficiencies (depletions) in H1.2 and H1.5 xxChIP-seq reads, compared to xChIP-seq. These observations suggest the existence of in situ transcription-related chromatin higher-order structures stabilized by formaldehyde.

CONCLUSION

Comparison of H1 xxChIP-seq to H1 xChIP-seq allows the development of hypotheses on the chromosomal localization of (stabilized) higher-order structure, indicated by the generation of "hidden" H1 epitopes following formaldehyde crosslinking. Changes in H1 epitope exposure surrounding averaged chromosomal binding sites or epigenetic modifications can also indicate whether these sites have chromatin higher-order structure. For example, comparison between averaged active or inactive promoter regions suggests that both regions can acquire stabilized higher-order structure with hidden H1 epitopes. However, the H1 xChIP-seq comparison cannot define their differences. Application of the xxChIP-seq versus H1 xChIP-seq method is particularly relevant to chromatin-associated proteins, such as linker histones, that play dynamic roles in establishing chromatin higher-order structure.

Rett syndrome-causing mutations compromise MeCP2-mediated liquid-liquid phase separation of chromatin

Rett syndrome (RTT), a severe postnatal neurodevelopmental disorder, is caused by mutations in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2). MeCP2 is a chromatin organizer regulating gene expression. RTT-causing mutations have been shown to affect this function. However, the mechanism by which MeCP2 organizes chromatin is unclear. In this study, we found that MeCP2 can induce compaction and liquid-liquid phase separation of nucleosomal arrays in vitro, and DNA methylation further enhances formation of chromatin condensates by MeCP2. Interestingly, RTT-causing mutations compromise MeCP2-mediated chromatin phase separation, while benign variants have little effect on this process. Moreover, MeCP2 competes with linker histone H1 to form mutually exclusive chromatin condensates in vitro and distinct heterochromatin foci in vivo. RTT-causing mutations reduce or even abolish the ability of MeCP2 to compete with histone H1 and to form chromatin condensates. Together, our results identify a novel mechanism by which phase separation underlies MeCP2-mediated heterochromatin formation and reveal the potential link between this process and the pathology of RTT.

Binding without folding - the biomolecular function of disordered polyelectrolyte complexes

Recent evidence shows that oppositely charged intrinsically disordered proteins (IDPs) can form high-affinity complexes that involve neither the formation of secondary or tertiary structure nor site-specific interactions between individual residues. Similar electrostatically dominated interactions have also been identified for positively charged IDPs binding to nucleic acids. These highly disordered polyelectrolyte complexes constitute an extreme case within the spectrum of biomolecular interactions involving disorder. Such interactions are likely to be widespread, since sequence analysis predicts proteins with highly charged disordered regions to be surprisingly numerous. Here, we summarize the insights that have emerged from the highly disordered polyelectrolyte complexes identified so far, and we highlight recent developments and future challenges in (i) establishing models for the underlying highly dynamic structural ensembles, (ii) understanding the novel binding mechanisms associated with them, and (iii) identifying the functional consequences.

Mesoscale Liquid Model of Chromatin Recapitulates Nuclear Order of Eukaryotes

The nuclear envelope segregates the genome of Eukaryota from the cytoplasm. Within the nucleus, chromatin is further compartmentalized into architectures that change throughout the lifetime of the cell. Epigenetic patterns along the chromatin polymer strongly correlate with chromatin compartmentalization and, accordingly, also change during the cell life cycle and at differentiation. Recently, it has been suggested that subnuclear chromatin compartmentalization might result from a process of liquid-liquid phase separation orchestrated by the epigenetic marking and operated by proteins that bind to chromatin. Here, we translate these observations into a diffuse interface model of chromatin, which we named the mesoscale liquid model of nucleus. Using this streamlined continuum model of the genome, we study the large-scale rearrangements of chromatin that happen at different stages of the growth and senescence of the cell and during nuclear inversion events. In particular, we investigate the role of droplet diffusion, fluctuations, and heterochromatin-lamina interactions during nuclear remodeling. Our results indicate that the physical process of liquid-liquid phase separation, together with surface effects, is sufficient to recapitulate much of the large-scale morphology and dynamics of chromatin along the life cycle of cells.

Disordered domains in chromatin-binding proteins

Chromatin comprises proteins, DNA and RNA, and its function is to condense and package the genome in a way that allows the necessary transactions such as transcription, replication and repair to occur in a highly organised and regulated manner. The packaging of chromatin is often thought of in a hierarchical fashion starting from the most basic unit of DNA packaging, the nucleosome, to the condensation of nucleosomal 'beads on a string' by linker histones to form the 30-nm fibre and eventually large chromatin domains. However, a picture of a more heterogeneous, dynamic and liquid-like assembly is emerging, in which intrinsically disordered proteins (IDPs) and proteins containing intrinsically disordered regions (IDRs) play a central role. Disorder features at all levels of chromatin organisation, from the histone tails, which are sites of extensive post-translational modification (PTM) that change the fate of the underlying genomic information, right through to transcription hubs, and the recently elucidated roles of IDPs and IDRs in the condensation of large regions of the genome through liquid-liquid phase separation.