During lagging strand chromatin replication, multiple Okazaki fragments (OFs) require processing and nucleosome assembly, but the mechanisms linking these processes remain unclear. Here, using transmission electron microscopy and rapid degradation of DNA ligase Cdc9, we observed flap structures accumulated on lagging strands, controlled by both Pol δ\'s strand displacement activity and Fen1\'s nuclease digestion. The distance between neighboring flap structures exhibits a regular pattern, indicative of matured OF length. While fen1Δ or enhanced strand displacement activities by polymerase δ (Pol δ; pol3exo-) minimally affect inter-flap distance, mutants affecting replication-coupled nucleosome assembly, such as cac1Δ and mcm2-3A, do significantly alter it. Deletion of Pol32, a subunit of DNA Pol δ, significantly increases this distance. Mechanistically, Pol32 binds to histone H3-H4 and is critical for nucleosome assembly on the lagging strand. Together, we propose that Pol32 establishes a connection between nucleosome assembly and the processing of OFs on lagging strands.

Asymmetric cell divisions (ACDs) generate two daughter cells with identical genetic information but distinct cell fates through epigenetic mechanisms. However, the process of partitioning different epigenetic information into daughter cells remains unclear. Here, we demonstrate that the nucleosome remodeling and deacetylase (NuRD) complex is asymmetrically segregated into the surviving daughter cell rather than the apoptotic one during ACDs in Caenorhabditis elegans. The absence of NuRD triggers apoptosis via the EGL-1-CED-9-CED-4-CED-3 pathway, while an ectopic gain of NuRD enables apoptotic daughter cells to survive. We identify the vacuolar H+-adenosine triphosphatase (V-ATPase) complex as a crucial regulator of NuRD\'s asymmetric segregation. V-ATPase interacts with NuRD and is asymmetrically segregated into the surviving daughter cell. Inhibition of V-ATPase disrupts cytosolic pH asymmetry and NuRD asymmetry. We suggest that asymmetric segregation of V-ATPase may cause distinct acidification levels in the two daughter cells, enabling asymmetric epigenetic inheritance that specifies their respective life-versus-death fates.

The chemical synthesis of homogeneously ubiquitylated histones is a powerful approach to decipher histone ubiquitylation-dependent epigenetic regulation. Among the various methods, α-halogen ketone-mediated conjugation chemistry has recently been an attractive strategy to generate single-monoubiquitylated histones for biochemical and structural studies. Herein, we report the use of this strategy to prepare not only dual- and even triple-monoubiquitylated histones but also diubiquitin-modified histones. We were surprised to find that the synthetic efficiencies of multi-monoubiquitylated histones were comparable to those of single-monoubiquitylated ones, suggesting that this strategy is highly tolerant to the number of ubiquitin monomers installed onto histones. The facile generation of a series of single-, dual-, and triple-monoubiquitylated H3 proteins enabled us to evaluate the influence of ubiquitylation patterns on the binding of DNA methyltransferase 1 (DNMT1) to nucleosomes. Our study highlights the potential of site-specific conjugation chemistry to generate chemically defined histones for epigenetic studies.

The testis-specific histone variant H3T plays a crucial role in chromatin reorganization during spermatogenesis by destabilizing nucleosomes. However, the structure basis for the nucleosome instability driven by H3T is not fully understand. In this study, we determinate the crystal structure of H3T-H4 in complex with histone chaperone ASF1a at 2.8 Å resolution. Our findings reveal that H3T-H4 binds ASF1a similarly to the conventional H3.1-H4 complex. However, significant structural differences are observed in the H3 α1 helix, the N- and C-terminal region of α2, and N-terminal region of L2. These differences are driven by H3T-specific residues, particularly Val111. Unlike the smaller Ala111 in H3.1, we find that bulkier residue Val111 fits well within the ASF1-H3T-H4 complex, but is difficult to arrange in nucleosome structure. Given that H3.1-Ala111/H3T-Val111 is located at the DNA binding and tetramerization interface of H3-H4, it is likely that Ala111Val substitution will lead to the instability of the corresponding area in nucleosome, contributing to instability of H3T-containing nucleosome. These structural findings may elucidate the role of H3T in chromatin reorganization during spermatogenesis.

BACKGROUND: Histone ubiquitination modification is emerging as a critical epigenetic mechanism involved in a range of biological processes. In vitro reconstitution of ubiquitinated nucleosomes is pivotal for elucidating the influence of histone ubiquitination on chromatin dynamics.
RESULTS: In this study, we introduce a Non-Denatured Histone Octamer Ubiquitylation (NDHOU) approach for generating ubiquitin or ubiquitin-like modified histone octamers. The method entails the co-expression and purification of histone octamers, followed by their chemical cross-linking to ubiquitin using 1,3-dibromoacetone. We demonstrate that nucleosomes reconstituted with these octamers display a high degree of homogeneity, rendering them highly compatible with in vitro biochemical assays. These ubiquitinated nucleosomes mimic physiological substrates in function and structure. Additionally, we have extended this method to cross-linking various histone octamers and three types of ubiquitin-like proteins.
CONCLUSIONS: Overall, our findings offer an efficient strategy for producing ubiquitinated nucleosomes, advancing biochemical and biophysical studies in the field of chromatin biology.

The SWI/SNF2 chromatin remodeling factor decreased DNA methylation 1 (DDM1) is essential for the silencing of transposable elements (TEs) in both euchromatic and heterochromatic regions. Here, we determined the cryo-EM structures of DDM1-nucleosomeH2A and DDM1-nucleosomeH2A.W complexes at near-atomic resolution in the presence of the ATP analog ADP-BeFx. The structures show that nucleosomal DNA is unwrapped more on the surface of the histone octamer containing histone H2A than that containing histone H2A.W. DDM1 embraces one DNA gyre of the nucleosome and interacts with the N-terminal tails of histone H4. Although we did not observe DDM1-H2A.W interactions in our structures, the results of the pull-down experiments suggest a direct interaction between DDM1 and the core region of histone H2A.W. Our work provides mechanistic insights into the heterochromatin remodeling process driven by DDM1 in plants.

OBJECTIVE: The predominant determinant of an unfavorable prognosis among Systemic Lupus Erythematosus (SLE) patients resides in the irreversible organ damage. This prospective cohort study aimed to identify the additional value of anti-nucleosome antibodies on organ damage accumulation in SLE patients.
METHODS: Based on the Chinese SLE Treatment and Research group (CSTAR) registry, demographic characteristics, autoantibodies profiles, and clinical manifestations were collected at baseline. Follow-up data were collected by reviewing clinical records.
RESULTS: Of 2481 SLE patients with full follow-up data, 663 (26.7%) were anti-nucleosome antibodies positive and 1668 (68.0%) were anti-dsDNA antibodies positive. 764 (30.8%) patients developed new organ damage during a mean follow-up of 4.31 ± 2.60 years. At baseline, patients with positive anti-nucleosome antibodies have a higher rate of lupus nephritis (50.7% vs 36.2%, p < .001). According to the multivariable Cox regression analysis, both anti-nucleosome (HR = 1.30, 95% CI, 1.09-1.54, p < .001) and anti-dsDNA antibodies (HR=1.68, 95% CI, 1.38-2.05, p < .001) were associated with organ damage accumulation. Anti-nucleosome (HR = 2.51, 95% CI, 1.81-3.46, p < .001) and anti-dsDNA antibodies (HR = 1.69, 95% CI, 1.39-2.06, p < .001) were independent predictors for renal damage. Furthermore, the combination of the two antibodies can provide more accurate information about renal damage in overall SLE patients (HR = 3.19, 95% CI, 2.49-4.10, p < .001) and patients with lupus nephritis at baseline (HR = 2.86, 95% CI, 2.29-3.57, p < .001).
CONCLUSIONS: Besides anti-dsDNA antibodies, anti-nucleosome antibodies can also provide information about organ damage accrual during follow-up. The ability of co-positivity of anti-nucleosome and anti-dsDNA antibodies in predicting renal damage may lead to additional benefits in the follow-up of these patients.

The RSF complex belongs to the ISWI chromatin-remodeling family and is composed of two subunits: RSF1 (remodeling and spacing factor 1) and SNF2h (sucrose nonfermenting protein 2 homolog). The RSF complex participates in nucleosome spacing and assembly, and subsequently promotes nucleosome maturation. Although SNF2h has been extensively studied in the last few years, the structural and functional properties of the remodeler RSF1 still remain vague. Here, a cryo-EM structure of the RSF-nucleosome complex is reported. The 3D model shows a two-lobe architecture of RSF, and the structure of the RSF-nucleosome (flanked with linker DNA) complex shows that the RSF complex moves the DNA away from the histone octamer surface at the DNA-entry point. Additionally, a nucleosome-sliding assay and a restriction-enzyme accessibility assay show that the RSF1 subunit may cause changes in the chromatin-remodeling properties of SNF2h. As a `nucleosome ruler\', the results of an RSF-dinucleosome binding affinity test led to the proposal that the critical distance that RSF `measures\' between two nucleosomes is about 24 base pairs.

The mammalian SWI/SNF-like BAF complexes play critical roles during animal development and pathological conditions. Previous gene deletion studies and characterization of human gene mutations implicate that the complexes both repress and activate a large number of genes. However, the direct function of the complexes in cells remains largely unclear due to the relatively long-term nature of gene deletion or natural mutation. Here we generate a mouse line by knocking in the auxin-inducible degron tag (AID) to the Smarca4 gene, which encodes BRG1, the essential ATPase subunit of the BAF complexes. We show that the tagged BRG1 can be efficiently depleted by osTIR1 expression and auxin treatment for 6 to 10 h in CD4 + T cells, hepatocytes, and fibroblasts isolated from the knock-in mice. The acute depletion of BRG1 leads to decreases in nascent RNAs and RNA polymerase II binding at a large number of genes, which are positively correlated with the loss of BRG1. Further, these changes are correlated with diminished accessibility at DNase I Hypersensitive Sites (DHSs) and p300 binding. The acute BRG1 depletion results in three major patterns of nucleosome shifts leading to narrower nucleosome spacing surrounding transcription factor motifs and at enhancers and transcription start sites (TSSs), which are correlated with loss of BRG1, decreased chromatin accessibility and decreased nascent RNAs. Acute depletion of BRG1 severely compromises the Trichostatin A (TSA) -induced histone acetylation, suggesting a substantial interplay between the chromatin remodeling activity of BRG1 and histone acetylation. Our data suggest BRG1 mainly plays a direct positive role in chromatin accessibility, RNAPII binding, and nascent RNA production by regulating nucleosome positioning and facilitating transcription factor binding to their target sites.

Histone chaperones and histone variants play crucial roles in DNA replication, gene transcription, and DNA repair in eukaryotes. Histone chaperones reversibly promote nucleosome assembly and disassembly by incorporating or evicting histones and histone variants to modulate chromatin accessibility, thereby altering the chromatin states and modulating DNA-related biological processes. Cofactors assist histone chaperones to target specific chromatin regions to regulate the exchange of histones and histone variants. In this review, we summarize recent progress in the interplay between histone variants and chaperones in plants. We discuss the structural basis of chaperone-histone complexes and the mechanisms of their cooperation in regulating gene transcription and plant development.