Project description:To avoid toxic histone overload, histone deposition and removal must be finely tuned. Following a series of functional studies in human, mouse and S. pombe, we show here that the AAA ATPase ATAD2 is a conserved mediator of histone removal and a regulator of histone deposition. In Atad2 knockout (KO) spermatogenic cells, the late-stage genome-wide eviction of histones and their replacement by protamines are significantly delayed. In S. pombe, deletion of abo1 leads to a dramatic decrease in cell growth, with the appearance of suppressor clones recovering normal growth. Identification of the corresponding suppressor mutations revealed that the causes of cell toxicity are mainly the deregulated activity of the histone chaperone HIRA and histone overload. We also show that, in Atad2 KO mouse ES cells, HIRA and FACT are trapped on nucleosomes at transcription start sites of active genes, resulting in histone overload and abnormal histone deposition on nucleosome-free regions. Overall, these data shed new light on a need for energy-consuming auxiliary factors, such as ATAD2, to maintain a balanced and dynamic histone chaperone basal activity and to avoid a deleterious histone overload.
Project description:Chromatin remodeling factors and histone chaperones were previously shown to cooperatively affect nucleosome assembly and disassembly processes in vitro. Here we show that S. pombe CHD remodellers, Hrp1 and Hrp3 physically interact with the histone chaperone Nap1. Genome wide analysis of Hrp1, Hrp3 and Nap1 occupancy, combined with nucleosome density measurements in respective mutants revealed that the CHD factors and Nap1 co-localized in particular to promoter regions where they remove nucleosomes near the transcriptional start site. Hrp1 and Hrp3 also regulate nucleosome density in coding regions where they have redundant roles to stimulate transcription. Previously, DNA replication dependent and independent nucleosome disassembly processes have been described. We found that nucleosome density increased in the hrp1 mutant in the absence of DNA replication. Finally, regions where nucleosome density increased in hrp1, hrp3 and nap1 mutants also showed nucleosome density and histone modification changes in HDAC and HAT mutants. Thus, this study revealed an important in vivo role for CHD remodellers and Nap1 in nucleosome disassembly at promoters and coding regions, which are linked to changes in histone acetylation. Keywords: ChIP on CHIP and expression profiling
Project description:The site-specific chromatin incorporation of eukaryotic histone variant H2A.Z is driven by the multi-component chromatin remodeling complex SWR1/SRCAP/ p400. The budding yeast SWR1 complex replaces the H2A-H2B dimer in the canonical nucleosome with the H2A.Z-H2B dimer, but the mechanism governing the directionality of H2A-to-H2A.Z exchange remains elusive. Here, we use single-molecule force spectroscopy to dissect the disassembly/ reassembly of H2A-nucleosome and H2A.Z-nucleosome. We find that the N-terminal 1-135 residues of yeast SWR1-complex-protein-2 (previously termed Swc2-Z) facilitate the disassembly of nucleosomes containing H2A but not H2A.Z. The Swc2-mediated nucleosome disassembly/reassembly requires the inherently unstable H2A-nucleosome, whose instability is conferred by three H2A α2-helix residues Gly47, Pro49 and Ile63 as they selectively weaken the structural rigidity of H2A-H2B dimer. It also requires Swc2-ZN (residues 1-37) that directly anchors to H2A-nucleosome and functions in the SWR1-catalyzed H2A.Z replacement in vitro and yeast H2A.Z deposition in vivo. Our findings providecrucial insights into how SWR1 complex discriminates between the H2A-nucleosome and H2A.Z-nucleosome, establishing a simple paradigm for the governace of unidirectional H2A.Z exchange.
Project description:Maintenance of the correct level and organization of nucleosomes is crucial for genome function. Here we uncover a role for a conserved bromodomain AAA-ATPase, Abo1, in maintenance of nucleosome architecture in fission yeast. Cells lacking abo1+ experience both a reduction and mis-positioning of nucleosomes at transcribed sequences in addition to increased intragenic transcription, phenotypes that are hallmarks of defective chromatin re-establishment behind RNA polymerase II. Abo1 is recruited to gene sequences and associates with histone H3 and the histone chaperone FACT. Furthermore, the distribution of Abo1 on chromatin is disturbed by impaired FACT function. The role of Abo1 extends to some promoters and also to silent heterochromatin. Abo1 is recruited to pericentromeric heterochromatin independently of the HP1 ortholog, Swi6, where it enforces proper nucleosome occupancy. Consequently, loss of Abo1 alleviates silencing and causes elevated chromosome mis-segregation. We suggest that Abo1 provides a histone chaperone function that maintains nucleosome architecture genome-wide. A chromatin-seq/MNase-seq approach called Chromatin Particle Spectrum Analysis (Kent et al., (2011) Nucleic Acids Res. 39:e26) was used to map and compare nucleosome position in wild-type (strain 972) and isogenic abo1 knock-out (strain HM463) fission yeast cells. For each strain, three independent in vivo MNase digest bio-reps were performed and the purified DNA pooled. CPSA was performed using paired-end mode Illumina technology with pooled samples multiplexed over two HiSeq2000 lanes. Each CPSA paired read describes a microcococcal nuclease (MNase) resistant DNA species from chromatin, with the insert-size equivalent to the size of DNA protection. For each strain type, two analysed data sets are provided here: one listing the genomic distribution of MNase-protected DNAs of 150bp (â150bp CPSA size classâ) and corresponding to mono-nucleosomes; the other listing the genomic distribution of MNase-protected DNAs of 300bp (â300bp CPSA size classâ) and corresponding to di-nucleosomes.
Project description:Maintenance of the correct level and organization of nucleosomes is crucial for genome function. Here we uncover a role for a conserved bromodomain AAA-ATPase, Abo1, in maintenance of nucleosome architecture in fission yeast. Cells lacking abo1+ experience both a reduction and mis-positioning of nucleosomes at transcribed sequences in addition to increased intragenic transcription, phenotypes that are hallmarks of defective chromatin re-establishment behind RNA polymerase II. Abo1 is recruited to gene sequences and associates with histone H3 and the histone chaperone FACT. Furthermore, the distribution of Abo1 on chromatin is disturbed by impaired FACT function. The role of Abo1 extends to some promoters and also to silent heterochromatin. Abo1 is recruited to pericentromeric heterochromatin independently of the HP1 ortholog, Swi6, where it enforces proper nucleosome occupancy. Consequently, loss of Abo1 alleviates silencing and causes elevated chromosome mis-segregation. We suggest that Abo1 provides a histone chaperone function that maintains nucleosome architecture genome-wide.
Project description:Chromatin replication requires tight coordination of nucleosome assembly machinery with DNA replication machinery. While significant progress has been made in characterizing histone chaperones in this process, the mechanism of whereby nucleosome assembly couples with DNA replication remains largely unknown. Here we show that replication protein A (RPA), a single-stranded DNA (ssDNA) binding protein that is essential for DNA replication provides a binding platform for H3-H4 deposition by histone chaperons and is required for nucleosome formation on nascent chromatin. RPA binds free histone H3-H4 but not nucleosomal histones, and a RPA coated ssDNA stimulates assembly of H3-H4 onto double strand DNA in vitro. RPA mutant with reduced H3-H4 binding exhibits synthetic genetic interaction with mutations at key factors involved in replication-coupled (RC) nucleosome assembly, and are defective in assembly of replicating DNA into nucleosomes in cells. These results reveal a novel function for RPA in nucleosome assembly and a mechanism whereby nucleosome assembly is coordinated with DNA replication.
Project description:Although the conserved AAA ATPase â bromodomain factor, ATAD2, has been described as a transcriptional co-activator upregulated in many cancers, its function remains poorly understood. Here, using a combination of ChIP-seq, ChIP-proteomics and RNA-seq experiments in embryonic stem cells, we found that Atad2 is an abundant nucleosome-bound protein present on active genes, associated with chromatin remodelling, DNA replication and DNA repair factors. A structural analysis of its bromodomain and subsequent investigations demonstrate that histone acetylation guides ATAD2 to chromatin, resulting in an overall increase of chromatin accessibility and histone dynamics, which is required for the proper activity of the highly expressed gene fraction of the genome. While in exponentially growing cells Atad2 appears dispensable for cell growth, in differentiating ES cells, Atad2 becomes critical in sustaining specific gene expression programs, controlling proliferation and differentiation. Altogether, this work defines Atad2âs function as a facilitator of general chromatin-templated activities such as transcription. Transcriptomic analyses comparing ES cells stably expressing anti-Atad2 shRNA versus cells expressing control shRNA, in day 3 LIF (-) differentiating ES cells (3 replicates for each condition) were performed using the Illumina MouseWG-6 v2.0 expression beadchip technology
Project description:Nuclear proteins bind chromatin to execute and regulate genome-templated processes. While structural and biochemical studies of individual nucleosome interactions have suggested that an acidic patch on the nucleosome disk surface may be a common site for recruitment to chromatin, the pervasiveness of acidic patch binding and whether other nucleosome surface binding hot-spots exist remains unclear. Here, we use nucleosome affinity proteomics with a library of nucleosomes that collectively disrupts all exposed histone surfaces to establish the universal principles of nucleosome binding. We find that the acidic patch and two adjacent surfaces are the primary hot-spots for nucleosome disk binding and are critical for the majority of nucleosome-protein interactions. In contrast, nearly half of the nucleosome disk surface participates only minimally in protein binding. In addition to establishing the fundamental principles of chromatin binding, our screen defines nucleosome surface requirements of nearly 300 nucleosome interacting proteins implicated in diverse nuclear processes including transcription, DNA damage repair, cell cycle regulation, and nuclear architecture. Building from our screen, we demonstrate that the Anaphase-Promoting Complex/Cyclosome directly binds the acidic patch and elucidate a redundant charge-based mechanism of acidic patch binding by nuclear pore protein ELYS. Overall, our interactome screen illuminates a highly competitive nucleosome binding hub for chromatin-targeted activities and curates a list of nucleosome interacting proteins that will enable mechanistic exploration of many unexpected chromatin-templated nuclear processes.
Project description:This is the microarray data accompanying the aforementioned manuscript. Summary: The histone chaperone Vps75 forms a complex with, and stimulates the activity of, the histone acetyltransferase Rtt109. However, Vps75 can also be isolated on its own and might therefore play a role in histone-related cellular processes independently of Rtt109. Using the E-MAP approach, we compared the genetic interaction profiles for VPS75 and RTT109 and found that, whereas deletion of RTT109 behaved like DNA replication/repair mutants, vps75Δ genetically interacted with genes linked to transcriptional regulation. Further genetic and biochemical experiments indicated an intimate relationship with RNA polymerase II, and chromatin immunoprecipitation showed that Vps75 is recruited to activated genes in an Rtt109-independent manner. Expression microarray analysis identified a limited number of genes whose normal expression depends on VPS75. Interestingly, histone H2B dynamics at some of these genes were consistent with a role for Vps75 as a histone H2A/H2B eviction factor during transcription-associated nucleosome disassembly. Indeed, reconstitution of nucleosome disassembly using the ATP-dependent chromatin remodeler Rsc and Vps75 showed that these proteins can cooperate to remove H2A/H2B dimers from nucleosomes. Together, these results indicate a role for Vps75 in nucleosome dynamics during active transcription, and that this function is likely to be independent of the histone acetyltransferase Rtt109. Keywords: Array-based; Chip-chip