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Search Results: 1 - 10 of 221806 matches for " Robin C Allshire "
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Silencing Mediated by the Schizosaccharomyces pombe HIRA Complex Is Dependent upon the Hpc2-Like Protein, Hip4
Holly E. Anderson,Alexander Kagansky,Josephine Wardle,Juri Rappsilber,Robin C. Allshire,Simon K. Whitehall
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0013488
Abstract: HIRA (or Hir) proteins are conserved histone chaperones that function in multi-subunit complexes to mediate replication-independent nucleosome assembly. We have previously demonstrated that the Schizosaccharomyces pombe HIRA proteins, Hip1 and Slm9, form a complex with a TPR repeat protein called Hip3. Here we have identified a new subunit of this complex.
Factors That Promote H3 Chromatin Integrity during Transcription Prevent Promiscuous Deposition of CENP-ACnp1 in Fission Yeast
Eun Shik Choi,Annelie Str?lfors,Sandra Catania,Araceli G. Castillo,J. Peter Svensson,Alison L. Pidoux,Karl Ekwall,Robin C. Allshire
PLOS Genetics , 2012, DOI: 10.1371/journal.pgen.1002985
Abstract: Specialized chromatin containing CENP-A nucleosomes instead of H3 nucleosomes is found at all centromeres. However, the mechanisms that specify the locations at which CENP-A chromatin is assembled remain elusive in organisms with regional, epigenetically regulated centromeres. It is known that normal centromeric DNA is transcribed in several systems including the fission yeast, Schizosaccharomyces pombe. Here, we show that factors which preserve stable histone H3 chromatin during transcription also play a role in preventing promiscuous CENP-ACnp1 deposition in fission yeast. Mutations in the histone chaperone FACT impair the maintenance of H3 chromatin on transcribed regions and promote widespread CENP-ACnp1 incorporation at non-centromeric sites. FACT has little or no effect on CENP-ACnp1 assembly at endogenous centromeres where CENP-ACnp1 is normally assembled. In contrast, Clr6 complex II (Clr6-CII; equivalent to Rpd3S) histone deacetylase function has a more subtle impact on the stability of transcribed H3 chromatin and acts to prevent the ectopic accumulation of CENP-ACnp1 at specific loci, including subtelomeric regions, where CENP-ACnp1 is preferentially assembled. Moreover, defective Clr6-CII function allows the de novo assembly of CENP-ACnp1 chromatin on centromeric DNA, bypassing the normal requirement for heterochromatin. Thus, our analyses show that alterations in the process of chromatin assembly during transcription can destabilize H3 nucleosomes and thereby allow CENP-ACnp1 to assemble in its place. We propose that normal centromeres provide a specific chromatin context that limits reassembly of H3 chromatin during transcription and thereby promotes the establishment of CENP-ACnp1 chromatin and associated kinetochores. These findings have important implications for genetic and epigenetic processes involved in centromere specification.
Plasticity of Fission Yeast CENP-A Chromatin Driven by Relative Levels of Histone H3 and H4
Araceli G Castillo equal contributor,Barbara G Mellone equal contributor,Janet F Partridge,William Richardson,Georgina L Hamilton,Robin C Allshire ,Alison L Pidoux
PLOS Genetics , 2007, DOI: 10.1371/journal.pgen.0030121
Abstract: The histone H3 variant CENP-A assembles into chromatin exclusively at centromeres. The process of CENP-A chromatin assembly is epigenetically regulated. Fission yeast centromeres are composed of a central kinetochore domain on which CENP-A chromatin is assembled, and this is flanked by heterochromatin. Marker genes are silenced when placed within kinetochore or heterochromatin domains. It is not known if fission yeast CENP-ACnp1 chromatin is confined to specific sequences or whether histone H3 is actively excluded. Here, we show that fission yeast CENP-ACnp1 can assemble on noncentromeric DNA when it is inserted within the central kinetochore domain, suggesting that in fission yeast CENP-ACnp1 chromatin assembly is driven by the context of a sequence rather than the underlying DNA sequence itself. Silencing in the central domain is correlated with the amount of CENP-ACnp1 associated with the marker gene and is also affected by the relative level of histone H3. Our analyses indicate that kinetochore integrity is dependent on maintaining the normal ratio of H3 and H4. Excess H3 competes with CENP-ACnp1 for assembly into central domain chromatin, resulting in less CENP-ACnp1 and other kinetochore proteins at centromeres causing defective kinetochore function, which is manifest as aberrant mitotic chromosome segregation. Alterations in the levels of H3 relative to H4 and CENP-ACnp1 influence the extent of DNA at centromeres that is packaged in CENP-ACnp1 chromatin and the composition of this chromatin. Thus, CENP-ACnp1 chromatin assembly in fission yeast exhibits plasticity with respect to the underlying sequences and is sensitive to the levels of CENP-ACnp1 and other core histones.
A DNA Polymerase α Accessory Protein, Mcl1, Is Required for Propagation of Centromere Structures in Fission Yeast
Toyoaki Natsume, Yasuhiro Tsutsui, Takashi Sutani, Elaine M. Dunleavy, Alison L. Pidoux, Hiroshi Iwasaki, Katsuhiko Shirahige, Robin C. Allshire, Fumiaki Yamao
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002221
Abstract: Specialized chromatin exists at centromeres and must be precisely transmitted during DNA replication. The mechanisms involved in the propagation of these structures remain elusive. Fission yeast centromeres are composed of two chromatin domains: the central CENP-ACnp1 kinetochore domain and flanking heterochromatin domains. Here we show that fission yeast Mcl1, a DNA polymerase α (Polα) accessory protein, is critical for maintenance of centromeric chromatin. In a screen for mutants that alleviate both central domain and outer repeat silencing, we isolated several cos mutants, of which cos1 is allelic to mcl1. The mcl1-101 mutation causes reduced CENP-ACnp1 in the central domain and an aberrant increase in histone acetylation in both domains. These phenotypes are also observed in a mutant of swi7+, which encodes a catalytic subunit of Polα. Mcl1 forms S-phase-specific nuclear foci, which colocalize with those of PCNA and Polα. These results suggest that Mcl1 and Polα are required for propagation of centromere chromatin structures during DNA replication.
Telomeric Repeats Facilitate CENP-ACnp1 Incorporation via Telomere Binding Proteins
Araceli G. Castillo, Alison L. Pidoux, Sandra Catania, Micka?l Durand-Dubief, Eun Shik Choi, Georgina Hamilton, Karl Ekwall, Robin C. Allshire
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0069673
Abstract: The histone H3 variant, CENP-A, is normally assembled upon canonical centromeric sequences, but there is no apparent obligate coupling of sequence and assembly, suggesting that centromere location can be epigenetically determined. To explore the tolerances and constraints on CENP-A deposition we investigated whether certain locations are favoured when additional CENP-ACnp1 is present in fission yeast cells. Our analyses show that additional CENP-ACnp1 accumulates within and close to heterochromatic centromeric outer repeats, and over regions adjacent to rDNA and telomeres. The use of minichromosome derivatives with unique DNA sequences internal to chromosome ends shows that telomeres are sufficient to direct CENP-ACnp1 deposition. However, chromosome ends are not required as CENP-ACnp1 deposition also occurs at telomere repeats inserted at an internal locus and correlates with the presence of H3K9 methylation near these repeats. The Ccq1 protein, which is known to bind telomere repeats and recruit telomerase, was found to be required to induce H3K9 methylation and thus promote the incorporation of CENP-ACnp1 near telomere repeats. These analyses demonstrate that at non-centromeric chromosomal locations the presence of heterochromatin influences the sites at which CENP-A is incorporated into chromatin and, thus, potentially the location of centromeres.
Genome-Wide Studies of Histone Demethylation Catalysed by the Fission Yeast Homologues of Mammalian LSD1
Michael Opel, David Lando, Carolina Bonilla, Sarah C. Trewick, Abdelhalim Boukaba, Julian Walfridsson, James Cauwood, Petra J.H. Werler, Antony M. Carr, Tony Kouzarides, Natalia V. Murzina, Robin C. Allshire, Karl Ekwall, Ernest D. Laue
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0000386
Abstract: In order to gain a more global view of the activity of histone demethylases, we report here genome-wide studies of the fission yeast SWIRM and polyamine oxidase (PAO) domain homologues of mammalian LSD1. Consistent with previous work we find that the two S. pombe proteins, which we name Swm1 and Swm2 (after SWIRM1 and SWIRM2), associate together in a complex. However, we find that this complex specifically demethylates lysine 9 in histone H3 (H3K9) and both up- and down-regulates expression of different groups of genes. Using chromatin-immunoprecipitation, to isolate fragments of chromatin containing either H3K4me2 or H3K9me2, and DNA microarray analysis (ChIP-chip), we have studied genome-wide changes in patterns of histone methylation, and their correlation with gene expression, upon deletion of the swm1+ gene. Using hyper-geometric probability comparisons we uncover genetic links between lysine-specific demethylases, the histone deacetylase Clr6, and the chromatin remodeller Hrp1. The data presented here demonstrate that in fission yeast the SWIRM/PAO domain proteins Swm1 and Swm2 are associated in complexes that can remove methyl groups from lysine 9 methylated histone H3. In vitro, we show that bacterially expressed Swm1 also possesses lysine 9 demethylase activity. In vivo, loss of Swm1 increases the global levels of both H3K9me2 and H3K4me2. A significant accumulation of H3K4me2 is observed at genes that are up-regulated in a swm1 deletion strain. In addition, H3K9me2 accumulates at some genes known to be direct Swm1/2 targets that are down-regulated in the swm1Δ strain. The in vivo data indicate that Swm1 acts in concert with the HDAC Clr6 and the chromatin remodeller Hrp1 to repress gene expression. In addition, our in vitro analyses suggest that the H3K9 demethylase activity requires an unidentified post-translational modification to allow it to act. Thus, our results highlight complex interactions between histone demethylase, deacetylase and chromatin remodelling activities in the regulation of gene expression.
Raf1 Is a DCAF for the Rik1 DDB1-Like Protein and Has Separable Roles in siRNA Generation and Chromatin Modification
Alessia Buscaino,Sharon A. White,Douglas R. Houston,Erwan Lejeune,Femke Simmer,Flavia de Lima Alves,Piyush T. Diyora,Takeshi Urano,Elizabeth H. Bayne,Juri Rappsilber,Robin C. Allshire
PLOS Genetics , 2012, DOI: 10.1371/journal.pgen.1002499
Abstract: Non-coding transcription can trigger histone post-translational modifications forming specialized chromatin. In fission yeast, heterochromatin formation requires RNAi and the histone H3K9 methyltransferase complex CLRC, composed of Clr4, Raf1, Raf2, Cul4, and Rik1. CLRC mediates H3K9 methylation and siRNA production; it also displays E3-ubiquitin ligase activity in vitro. DCAFs act as substrate receptors for E3 ligases and may couple ubiquitination with histone methylation. Here, structural alignment and mutation of signature WDxR motifs in Raf1 indicate that it is a DCAF for CLRC. We demonstrate that Raf1 promotes H3K9 methylation and siRNA amplification via two distinct, separable functions. The association of the DCAF Raf1 with Cul4-Rik1 is critical for H3K9 methylation, but dispensable for processing of centromeric transcripts into siRNAs. Thus the association of a DCAF, Raf1, with its adaptor, Rik1, is required for histone methylation and to allow RNAi to signal to chromatin.
The disease business
Robin C May
Genome Biology , 2000, DOI: 10.1186/gb-2000-1-5-reports4021
Abstract: The world of host-pathogen interaction is a complex and fascinating one. By focusing on a diverse variety of pathogens, this minisymposium dramatically illustrated the extremely elaborate specializations that have evolved during the long-running battle between pathogen and host.The proceedings opened with a familiar pathogen, Escherichia coli, demonstrating a familiar problem, the infection of epithelia. As the first line of defense, epithelia regularly repel the microscopic pirates that seek a home in the centrally heated comfort of the human body. Why, then, are pathogens vigorously ejected by some epithelia, but only weakly rebuffed by others?Staffan Normark and colleagues (Karolinska Institute, Stockholm, Sweden) addressed this question by studying the interaction between E. coli and epithelial cells derived from bladder and kidney. As most urinary tract infections are caused by faecal E. coli, they reasoned that the bladder would be exposed to these opportunistic pathogens far more frequently than the kidney. Hence the bladder epithelium might be expected to have evolved more effective defences than the kidney, which was indeed exactly what Normark found. When exposed to bacterial lipopolysaccharide, epithelial cells from the bladder mount a vigorous inflammatory response, whereas the response of kidney epithelia is much weaker. This coincides neatly with the observation that kidney infections are far more likely to become chronic than those in the bladder.From the familiar ground of E. coli, the session moved to newer territory - the little-known pathogen Bartonella. Several members of this genus cause disease, ranging from localized inflammation (B. henselae) to fatal haemolytic anaemia (B. quintana). Christoph Dehio (University of Basel, Switzerland) presented his lab's recent progress in understanding their mechanism of infection. The pathogenic capacity of Bartonella stems from its ability to invade endothelia and red blood cells. After attaching to the en
Conformal Powers of the Laplacian via Stereographic Projection
C. Robin Graham
Symmetry, Integrability and Geometry : Methods and Applications , 2007,
Abstract: A new derivation is given of Branson's factorization formula for the conformally invariant operator on the sphere whose principal part is the k-th power of the scalar Laplacian. The derivation deduces Branson's formula from knowledge of the corresponding conformally invariant operator on Euclidean space (the k-th power of the Euclidean Laplacian) via conjugation by the stereographic projection mapping.
Galaxy modelling through stellar population synthesis
Robin A.C.
EPJ Web of Conferences , 2012, DOI: 10.1051/epjconf/20121909003
Abstract: In recent years, models of the Galaxy based on the spirit of population synthesis have considerably helped to improve our knowledge on the Galaxy and its formation scenario. I describe the different approaches used by several teams, how they differ, and present the significant advances which have been made through this approach using two examples: the thick disc and the bulge/bar populations.
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