Molecular and structural basis of the chromatin remodeling activity by Arabidopsis DDM1.

The histone H2A variant H2A.W occupies transposons and thus prevents access to them in Arabidopsis thaliana. H2A.

H3K4me1 recruits DNA repair proteins in plants.

DNA repair proteins can be recruited by their histone reader domains to specific epigenomic features, with consequences on intragenomic mutation rate variation. Here, we investigated H3K4me1-associated hypomutation in plants. We first examined 2 proteins which, in plants, contain Tudor histone reader domains: PRECOCIOUS DISSOCIATION OF SISTERS 5 (PDS5C), involved in homology-directed repair, and MUTS HOMOLOG 6 (MSH6), a mismatch repair protein.

Histone variants shape chromatin states in Arabidopsis.

How different intrinsic sequence variations and regulatory modifications of histones combine in nucleosomes remain unclear. To test the importance of histone variants in the organization of chromatin we investigated how histone variants and histone modifications assemble in the genome. We showed that a limited number of chromatin states divide euchromatin and heterochromatin into several subdomains.

Thiocholine-Mediated One-Pot Peptide Ligation and Desulfurization.

Thiol catalysts are essential in native chemical ligation (NCL) to increase the reaction efficiency. In this paper, we report the use of thiocholine in chemical protein synthesis, including NCL-based peptide ligation and metal-free desulfurization. Evaluation of thiocholine peptide thioester in terms of NCL and hydrolysis kinetics revealed its practical utility, which was comparable to that of other alkyl thioesters.

Elongation factor 1 is a component of the Arabidopsis RNA polymerase II elongation complex and associates with a subset of transcribed genes.

Elongation factors modulate the efficiency of mRNA synthesis by RNA polymerase II (RNAPII) in the context of chromatin, thus contributing to implement proper gene expression programmes. The zinc-finger protein elongation factor 1 (ELF1) is a conserved transcript elongation factor (TEF), whose molecular function so far has not been studied in plants. Using biochemical approaches, we examined the interaction of Arabidopsis ELF1 with DNA and histones in vitro and with the RNAPII elongation complex in vivo.

Histone renegades: Unusual H2A histone variants in plants and animals.

H2A variants are histones that carry out specialized nucleosome function during the eukaryote genome packaging. Most genes encoding H2A histone variants arose in the distant past, and have highly conserved domains and structures. Yet, novel H2A variants have continued to arise throughout the radiation of eukaryotes and disturbed the apparent tranquility of nucleosomes.

Phosphorylation of the FACT histone chaperone subunit SPT16 affects chromatin at RNA polymerase II transcriptional start sites in Arabidopsis.

The heterodimeric histone chaperone FACT, consisting of SSRP1 and SPT16, contributes to dynamic nucleosome rearrangements during various DNA-dependent processes including transcription. In search of post-translational modifications that may regulate the activity of FACT, SSRP1 and SPT16 were isolated from Arabidopsis cells and analysed by mass spectrometry. Four acetylated lysine residues could be mapped within the basic C-terminal region of SSRP1, while three phosphorylated serine/threonine residues were identified in the acidic C-terminal region of SPT16.

The chromatin remodeler DDM1 prevents transposon mobility through deposition of histone variant H2A.W.

Mobile transposable elements (TEs) not only participate in genome evolution but also threaten genome integrity. In healthy cells, TEs that encode all of the components that are necessary for their mobility are specifically silenced, yet the precise mechanism remains unknown. Here, we characterize the mechanism used by a conserved class of chromatin remodelers that prevent TE mobility.

A Synthetic Approach to Reconstruct the Evolutionary and Functional Innovations of the Plant Histone Variant H2A.W.

Diversification of histone variants is marked by the acquisition of distinct motifs and functional properties through convergent evolution. H2A variants are distinguished by specific C-terminal motifs and tend to be segregated within defined domains of the genome. Whether evolution of these motifs pre-dated the evolution of segregation mechanisms or vice versa has remained unclear.

The evolution and functional divergence of the histone H2B family in plants.

Chromatin regulation of eukaryotic genomes depends on the formation of nucleosome complexes between histone proteins and DNA. Histone variants, which are diversified by sequence or expression pattern, can profoundly alter chromatin properties. While variants in histone H2A and H3 families are well characterized, the extent of diversification of histone H2B proteins is less understood.

Structural Studies of Overlapping Dinucleosomes in Solution.

An overlapping dinucleosome (OLDN) is a structure composed of one hexasome and one octasome and appears to be formed through nucleosome collision promoted by nucleosome remodeling factor(s). In this study, the solution structure of the OLDN was investigated through the integration of small-angle x-ray and neutron scattering (SAXS and SANS, respectively), computer modeling, and molecular dynamics simulations. Starting from the crystal structure, we generated a conformational ensemble based on normal mode analysis and searched for the conformations that reproduced the SAXS and SANS scattering curves well.

Transcription factor DUO1 generated by neo-functionalization is associated with evolution of sperm differentiation in plants.

Evolutionary mechanisms underlying innovation of cell types have remained largely unclear. In multicellular eukaryotes, the evolutionary molecular origin of sperm differentiation is unknown in most lineages. Here, we report that in algal ancestors of land plants, changes in the DNA-binding domain of the ancestor of the MYB transcription factor DUO1 enabled the recognition of a new cis-regulatory element.

Corrigendum to: Contribution of histone N-terminal tails to the structure and stability of nucleosomes.

[This corrects the article DOI: 10.1016/j.fob.

Histone H2A variants confer specific properties to nucleosomes and impact on chromatin accessibility.

In eukaryotes, variants of core histone H2A are selectively incorporated in distinct functional domains of chromatin and are distinguished by conserved sequences of their C-terminal tail, the L1 loop and the docking domain, suggesting that each variant confers specific properties to the nucleosome. Chromatin of flowering plants contains four types of H2A variants, which biochemical properties have not been characterized. We report that in contrast with animals, in Arabidopsis thaliana H2A variants define only four major types of homotypic nucleosomes containing exclusively H2A, H2A.

Structural Diversity of Nucleosomes Characterized by Native Mass Spectrometry.

Histone tails, which protrude from nucleosome core particles (NCPs), play crucial roles in the regulation of DNA transcription, replication, and repair. In this study, structural diversity of nucleosomes was investigated in detail by analyzing the observed charge states of nucleosomes reconstituted with various lengths of DNA using positive-mode electrospray ionization mass spectrometry (ESI-MS) and molecular dynamics (MD) simulation. Here, we show that canonical NCPs, having 147 bp DNA closely wrapped around a histone octamer, can be classified into three groups by charge state, with the least-charged group being more populated than the highly charged and intermediate groups.

Synthetic Posttranslational Modifications: Chemical Catalyst-Driven Regioselective Histone Acylation of Native Chromatin.

Posttranslational modifications (PTMs) of histones play an important role in the complex regulatory mechanisms governing gene transcription, and their dysregulation can cause diseases such as cancer. The lack of methods for site-selectively modifying native chromatin, however, limits our understanding of the functional roles of a specific histone PTM, not as a single mark, but in the intertwined PTM network. Here, we report a synthetic catalyst DMAP-SH (DSH), which activates chemically stable thioesters (including acetyl-CoA) under physiological conditions and transfers various acyl groups to the proximate amino groups.

Genome-Wide Profiling of Histone Modifications and Histone Variants in Arabidopsis thaliana and Marchantia polymorpha.

Histone modifications and histone variants barcode the genome and play major roles in epigenetic regulations. Chromatin immunoprecipitation (ChIP) coupled with next-generation sequencing (NGS) is a well-established method to investigate the landscape of epigenetic marks at a genomic level. Here, we describe procedures for conducting ChIP, subsequent NGS library construction, and data analysis on histone modifications and histone variants in Arabidopsis thaliana.

Crystal structure of the overlapping dinucleosome composed of hexasome and octasome.

Nucleosomes are dynamic entities that are repositioned along DNA by chromatin remodeling processes. A nucleosome repositioned by the switch-sucrose nonfermentable (SWI/SNF) remodeler collides with a neighbor and forms the intermediate "overlapping dinucleosome." Here, we report the crystal structure of the overlapping dinucleosome, in which two nucleosomes are associated, at 3.

Crystal Structure and Characterization of Novel Human Histone H3 Variants, H3.6, H3.7, and H3.8.

Non-allelic histone variants are considered as epigenetic factors that regulate genomic DNA functions in eukaryotic chromosomes. In this study, we identified three new human histone H3 variants (named H3.6, H3.

Polymorphism of apyrimidinic DNA structures in the nucleosome.

Huge amounts (>10,000/day) of apurinic/apyrimidinic (AP) sites are produced in genomes, but their structures in chromatin remain undetermined. We determined the crystal structure of the nucleosome containing AP-site analogs at two symmetric sites, which revealed structural polymorphism: one forms an inchworm configuration without an empty space at the AP site, and the other forms a B-form-like structure with an empty space and the orphan base. This unexpected inchworm configuration of the AP site is important to understand the AP DNA repair mechanism, because it may not be recognized by the major AP-binding protein, APE1, during the base excision repair process.

Structure and function of human histone H3.Y nucleosome.

Histone H3.Y is a primate-specific, distant H3 variant. It is evolutionarily derived from H3.

C-terminal acidic domain of histone chaperone human NAP1 is an efficient binding assistant for histone H2A-H2B, but not H3-H4.

Nucleosome assembly protein 1 (NAP1) binds both the (H3-H4)2 tetramer and two H2A-H2B dimers, mediating their sequential deposition on DNA. NAP1 contains a C-terminal acidic domain (CTAD) and a core domain that promotes dimer formation. Here, we have investigated the roles of the core domain and CTAD of human NAP1 in binding to H2A-H2B and H3-H4 by isothermal calorimetry and native mass spectrometry and compared them with the roles of yeast NAP1.

Crystal structure of the nucleosome containing ultraviolet light-induced cyclobutane pyrimidine dimer.

The cyclobutane pyrimidine dimer (CPD) is induced in genomic DNA by ultraviolet (UV) light. In mammals, this photolesion is primarily induced within nucleosomal DNA, and repaired exclusively by the nucleotide excision repair (NER) pathway. However, the mechanism by which the CPD is accommodated within the nucleosome has remained unknown.