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Nils Krietenstein, Megha Wal, Shinya Watanabe, Bongsoo Park, Craig L Peterson, B Franklin Pugh, Philipp Korber
Chromatin remodelers regulate genes by organizing nucleosomes around promoters, but their individual contributions are obfuscated by the complex in vivo milieu of factor redundancy and indirect effects. Genome-wide reconstitution of promoter nucleosome organization with purified proteins resolves this problem and is therefore a critical goal. Here, we reconstitute four stages of nucleosome architecture using purified components: yeast genomic DNA, histones, sequence-specific Abf1/Reb1, and remodelers RSC, ISW2, INO80, and ISW1a...
October 20, 2016: Cell
Prabodh Kapoor, Xuetong Shen
Using a reconstituted system containing genomic DNA and purified proteins from yeast, Krietenstein et al. uncover the direct contributions of key factors in nucleosome positioning and conceptualize the process into four distinct stages.
October 20, 2016: Cell
Soya Shinkai, Tadasu Nozaki, Kazuhiro Maeshima, Yuichi Togashi
The mammalian genome is organized into submegabase-sized chromatin domains (CDs) including topologically associating domains, which have been identified using chromosome conformation capture-based methods. Single-nucleosome imaging in living mammalian cells has revealed subdiffusively dynamic nucleosome movement. It is unclear how single nucleosomes within CDs fluctuate and how the CD structure reflects the nucleosome movement. Here, we present a polymer model wherein CDs are characterized by fractal dimensions and the nucleosome fibers fluctuate in a viscoelastic medium with memory...
October 2016: PLoS Computational Biology
Jason T Huff, Daniel Zilberman, Scott W Roy
The discovery of introns four decades ago was one of the most unexpected findings in molecular biology. Introns are sequences interrupting genes that must be removed as part of messenger RNA production. Genome sequencing projects have shown that most eukaryotic genes contain at least one intron, and frequently many. Comparison of these genomes reveals a history of long evolutionary periods during which few introns were gained, punctuated by episodes of rapid, extensive gain. However, although several detailed mechanisms for such episodic intron generation have been proposed, none has been empirically supported on a genomic scale...
October 19, 2016: Nature
Buki Kwon, Palinda Ruvan Munashingha, Yong-Keol Shin, Chul-Hwan Lee, Bing Li, Yeon-Soo Seo
Highly conserved eukaryotic histones are polybasic proteins that package DNA into nucleosomes, a building block of chromatin, allowing extremely long DNA molecules to form compact and discrete chromosomes. The histone N-terminal tails that extend from the nucleosome core act as docking sites for many proteins through diverse posttranslational modifications, regulating various DNA transactions. In this report, we present evidence that the nucleosomes can positively regulate the enzymatic activity of Rad27 (yeast Fen1), a major processing enzyme important for Okazaki fragment in eukaryotes...
October 19, 2016: FEBS Journal
John M Hinz, Marian F Laughery, John J Wyrick
Nucleosomes affect Cas9 binding and activity at on-target sites, but their impact at off-target sites is unknown. To investigate how nucleosomes affect Cas9 cleavage at off-target sites in vitro, we used a single guide RNA (sgRNA) that has been previously shown to efficiently direct Cas9 cleavage at the edge of the strongly positioned 601 nucleosome. Our data indicate that single mismatches between the sgRNA and DNA target have relatively little effect on Cas9 cleavage of naked DNA substrates, but strongly inhibit cleavage of nucleosome substrates, particularly when the mismatch is in the sgRNA 'seed' region...
October 18, 2016: Journal of Biological Chemistry
Vasily M Studitsky, Ekaterina V Nizovtseva, Alexey K Shaytan, Donal S Luse
Packaging of DNA into chromatin affects all processes on DNA. Nucleosomes present a strong barrier to transcription, raising important questions about the nature and the mechanisms of overcoming the barrier. Recently it was shown that DNA sequence, DNA-histone interactions and backtracking by RNA polymerase II (Pol II) all contribute to formation of the barrier. After partial uncoiling of nucleosomal DNA from histone octamer by Pol II and backtracking of the enzyme, nucleosomal DNA recoils on the octamer, locking Pol II in the arrested state...
2016: Biochemistry & Molecular Biology Journal
Naoshi Nishida, Masatoshi Kudo
Accumulation of genetic and epigenetic alterations is a hallmark of cancer genomes, including those in hepatocellular carcinoma (HCC). Particularly, in human HCC, epigenetic changes are more frequently observed than genetic changes in a variety of cancer-related genes, suggesting a potential role for epigenetic alterations during hepatocarcinogenesis. Several environmental factors, such as inflammation, obesity, and steatosis, are reported to affect the epigenetic status in hepatocytes, which could play a role in HCC development...
2016: Digestive Diseases
Michael Saul, Petra Majdak, Samuel Perez, Matthew Reilly, Theodore Garland, Justin S Rhodes
Though exercise is critical for health, many lack the motivation to exercise, and it is unclear how motivation might be increased. To uncover the molecular underpinnings of increased motivation for exercise, we analyzed the transcriptome of the striatum in four mouse lines selectively bred for high voluntary wheel running and four non-selected control lines. The striatum was dissected and RNA was extracted and sequenced from four individuals of each line. We found multiple genes and gene systems with strong relationships to both selection and running history over the previous 6 days...
October 17, 2016: Genes, Brain, and Behavior
Saeed Izadi, Ramu Anandakrishnan, Alexey V Onufriev
Molecular Dynamics (MD) simulations based on the implicit solvent generalized Born (GB) models can provide significant computational advantages over the traditional explicit solvent simulations. However, the standard GB becomes prohibitively expensive for all-atom simulations of large structures; the model scales poorly, ~n^2, with the number of solute atoms. Here we combine our recently developed Optimal Point Charge Approximation (OPCA) with the Hierarchical Charge Partitioning (HCP) approximation to present an ~n log n multi-scale, yet fully atomistic, GB model (GB-HCPO)...
October 17, 2016: Journal of Chemical Theory and Computation
Julian Lange, Shintaro Yamada, Sam E Tischfield, Jing Pan, Seoyoung Kim, Xuan Zhu, Nicholas D Socci, Maria Jasin, Scott Keeney
Heritability and genome stability are shaped by meiotic recombination, which is initiated via hundreds of DNA double-strand breaks (DSBs). The distribution of DSBs throughout the genome is not random, but mechanisms molding this landscape remain poorly understood. Here, we exploit genome-wide maps of mouse DSBs at unprecedented nucleotide resolution to uncover previously invisible spatial features of recombination. At fine scale, we reveal a stereotyped hotspot structure-DSBs occur within narrow zones between methylated nucleosomes-and identify relationships between SPO11, chromatin, and the histone methyltransferase PRDM9...
October 20, 2016: Cell
Samuel Corless, Nick Gilbert
Disruptions in chromatin structure are necessary for the regulation of eukaryotic genomes, from remodelling of nucleosomes at the base pair level through to large-scale chromatin domains that are hundreds of kilobases in size. RNA polymerase is a powerful motor which, prevented from turning with the tight helical pitch of the DNA, generates over-wound DNA ahead of itself and under-wound DNA behind. Mounting evidence supports a central role for transcription-dependent DNA supercoiling in disrupting chromatin structure at all scales...
2016: Biophysical Reviews
Gayan Senavirathne, Santosh K Mahto, Jeungphill Hanne, Daniel O'Brian, Richard Fishel
Wrapping of genomic DNA into nucleosomes poses thermodynamic and kinetic barriers to biological processes such as replication, transcription, repair and recombination. Previous biochemical studies have demonstrated that in the presence of adenosine triphosphate (ATP) the human RAD51 (HsRAD51) recombinase can form a nucleoprotein filament (NPF) on double-stranded DNA (dsDNA) that is capable of unwrapping the nucleosomal DNA from the histone octamer (HO). Here, we have used single molecule Förster Resonance Energy Transfer (smFRET) to examine the real time nucleosome dynamics in the presence of the HsRAD51 NPF...
October 13, 2016: Nucleic Acids Research
Nathalie Dehne, Bernhard Brüne
Hypoxia, by activating transcription factors induces transcription of some genes but it also reduces mRNA synthesis by mechanisms that are poorly defined. Activation of human macrophages with interleukin (IL)-4 showed that up-regulation of some IL-4 target genes was reduced when macrophages were incubated at 1% oxygen. Hypoxia impaired induction of chemokine (C-C motif) ligand 18 (CCL18), although IL-4-induced DNA binding of the transcription factor STAT6 remained intact. In contrast, induction of serine peptidase inhibitor, Kunitz type (SPINT)2, another IL-4/STAT6 target gene, was not affected by hypoxia...
October 11, 2016: Biochimica et Biophysica Acta
Miriam Laxa
Catalase 2 (CAT2) plays an important role in the detoxification of hydrogen peroxide released either during photorespiration or as a consequence of biotic and abiotic stress as well as in the initiation of senescence. To date, our understanding of the regulation of CAT2 gene expression is rather poor. Chromatin immunoprecipitation experiments revealed that a wide region of the CAT2 promoter is nucleosome depleted, reflecting the ability to rapidly respond to changing environmental and stress conditions and, thus, adjusting the transcript levels of CAT2...
October 12, 2016: Plant Molecular Biology
Cornelia G Spruijt, Martijn S Luijsterburg, Roberta Menafra, Rik G H Lindeboom, Pascal W T C Jansen, Raghu Ram Edupuganti, Marijke P Baltissen, Wouter W Wiegant, Moritz C Voelker-Albert, Filomena Matarese, Anneloes Mensinga, Ina Poser, Harmjan R Vos, Hendrik G Stunnenberg, Haico van Attikum, Michiel Vermeulen
NuRD (nucleosome remodeling and histone deacetylase) is a versatile multi-protein complex with roles in transcription regulation and the DNA damage response. Here, we show that ZMYND8 bridges NuRD to a number of putative DNA-binding zinc finger proteins. The MYND domain of ZMYND8 directly interacts with PPPLΦ motifs in the NuRD subunit GATAD2A. Both GATAD2A and GATAD2B exclusively form homodimers and define mutually exclusive NuRD subcomplexes. ZMYND8 and NuRD share a large number of genome-wide binding sites, mostly active promoters and enhancers...
October 11, 2016: Cell Reports
Joshua Lequieu, Andrés Córdoba, David C Schwartz, Juan J de Pablo
Nucleosomes form the basic unit of compaction within eukaryotic genomes, and their locations represent an important, yet poorly understood, mechanism of genetic regulation. Quantifying the strength of interactions within the nucleosome is a central problem in biophysics and is critical to understanding how nucleosome positions influence gene expression. By comparing to single-molecule experiments, we demonstrate that a coarse-grained molecular model of the nucleosome can reproduce key aspects of nucleosome unwrapping...
September 28, 2016: ACS Central Science
Tsung-Han S Hsieh, Geoffrey Fudenberg, Anton Goloborodko, Oliver J Rando
We present Micro-C XL, an improved method for analysis of chromosome folding at mononucleosome resolution. Using long crosslinkers and isolation of insoluble chromatin, Micro-C XL increases signal-to-noise ratio. Micro-C XL maps of budding and fission yeast genomes capture both short-range chromosome fiber features such as chromosomally interacting domains and higher order features such as centromere clustering. Micro-C XL provides a single assay to interrogate chromosome folding at length scales from the nucleosome to the full genome...
October 10, 2016: Nature Methods
Michael Tsabar, Wade M Hicks, Olga Tsaponina, James E Haber
Homologous recombination (HR) is an evolutionarily conserved pathway in eukaryotes that repairs a double-strand break (DSB) by copying homologous sequences from a sister chromatid, a homologous chromosome or an ectopic location. Recombination is challenged by the packaging of DNA into nucleosomes, which may impair the process at many steps, from resection of the DSB ends to the re-establishement of nucleosomes after repair. However, nucleosome dynamics during DSB repair have not been well described, primarily because of a lack of well-ordered nucleosomes around a DSB...
September 28, 2016: DNA Repair
Peng Mao, John J Wyrick, Steven A Roberts, Michael J Smerdon
UV radiation induces photolesions that distort the DNA double helix and, if not repaired, can cause severe biological consequences, including mutagenesis or cell death. In eukaryotes, both the formation and repair of UV damage occur in the context of chromatin, in which genomic DNA is packaged with histones into nucleosomes and higher-order chromatin structures. Here, we review how chromatin impacts the formation of UV photoproducts in eukaryotic cells. We describe the initial discovery that nucleosomes and other DNA-binding proteins induce characteristic 'photofootprints' during the formation of UV photoproducts...
September 26, 2016: Photochemistry and Photobiology
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