Project description:Actin-related proteins are ubiquitous components of chromatin remodelers, and are conserved from yeast to man. We have examined the role of the budding yeast actin-related protein Arp6 in gene expression, both as a component of the SWR1 complex (SWR-C) and in its absence. We mapped Arp6-binding sites genome-wide using chromatin immunoprecipitation in mutant and wild-type cells. We find that the majority of Arp6-binding sites in euchromatin coincide with binding sites of Swr1, the catalytic subunit of SWR-C, and with the histone H2A variant Htz1. However, the remaining Arp6 binding in telomeres, centromeres, and the promoters of ribosomal protein (RP) genes are independent of Swr1 and Htz1 deposition. We show that Arp6 can position chromatin at nuclear pores, and is required for the pore association of the RP genes to which it binds. This anchoring is also independent of Swr1. Loss of Arp6, but not Htz1, leads to an up-regulation of RP genes and loss of relocalization. This is in contrast to the Htz1-mediated pore-association of GAL1, for which loss of Arp6 impairs activation. Given that Arp6 is required for SWR-C dependent deposition of Htz1, we conclude that Arp6 contributes to both H2AZ-dependent and H2AZ-independent association with nuclear pores and subsequent effects on gene expression. These data illustrate how nuclear actin-related proteins contribute to the long-range organization of chromatin domains in the interphase nucleus. Four replicates for the arp6 deletion mutant and three replicates for the swr1 deletion mutant compared to wild-type.
Project description:Actin-related proteins are ubiquitous components of chromatin remodelers, and are conserved from yeast to man. We have examined the role of the budding yeast actin-related protein Arp6 in gene expression, both as a component of the SWR1 complex (SWR-C) and in its absence. We mapped Arp6-binding sites genome-wide using chromatin immunoprecipitation in mutant and wild-type cells. We find that the majority of Arp6-binding sites in euchromatin coincide with binding sites of Swr1, the catalytic subunit of SWR-C, and with the histone H2A variant Htz1. However, the remaining Arp6 binding in telomeres, centromeres, and the promoters of ribosomal protein (RP) genes are independent of Swr1 and Htz1 deposition. We show that Arp6 can position chromatin at nuclear pores, and is required for the pore association of the RP genes to which it binds. This anchoring is also independent of Swr1. Loss of Arp6, but not Htz1, leads to an up-regulation of RP genes and loss of relocalization. This is in contrast to the Htz1-mediated pore-association of GAL1, for which loss of Arp6 impairs activation. Given that Arp6 is required for SWR-C dependent deposition of Htz1, we conclude that Arp6 contributes to both H2AZ-dependent and H2AZ-independent association with nuclear pores and subsequent effects on gene expression. These data illustrate how nuclear actin-related proteins contribute to the long-range organization of chromatin domains in the interphase nucleus.
Project description:Deposition of histone variant H2A.Z by the SWR1 chromatin-remodeling complex is critical for the appropriate expression of many genes in eukaryotes, yet, despite its importance, the composition of the Arabidopsis SWR1 complex has not been thoroughly analyzed. Here we have identified the interacting partners of a conserved Arabidopsis SWR1 subunit, actin-related protein 6 (ARP6). We isolated 9 predicted components, identifying subunits implicated in histone acetylation and interacting partners implicated in chromatin biology. We found that the methyl-CpG-binding domain 9 (MBD9) subunit functioned synergistically with ARP6 to control flowering time. MBD9, in combination with ARP6, was involved in the SWR1-mediated incorporation of the majority of H2A.Z. MBD6 was further required for deposition of H2A.Z at a distinct subset of loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5’ of genes containing high levels of activating histone marks. Our data suggests a model for MBD9 in recruiting the SWR1 complex to open chromatin of actively transcribing genes.
Project description:Deposition of histone variant H2A.Z by the SWR1 chromatin-remodeling complex is critical for the appropriate expression of many genes in eukaryotes, yet, despite its importance, the composition of the Arabidopsis SWR1 complex has not been thoroughly analyzed. Here we have identified the interacting partners of a conserved Arabidopsis SWR1 subunit, actin-related protein 6 (ARP6). We isolated 9 predicted components, identifying subunits implicated in histone acetylation and interacting partners implicated in chromatin biology. We found that the methyl-CpG-binding domain 9 (MBD9) subunit functioned synergistically with ARP6 to control flowering time. MBD9, in combination with ARP6, was involved in the SWR1-mediated incorporation of the majority of H2A.Z. MBD6 was further required for deposition of H2A.Z at a distinct subset of loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5’ of genes containing high levels of activating histone marks. Our data suggests a model for MBD9 in recruiting the SWR1 complex to open chromatin of actively transcribing genes.
Project description:Deposition of histone variant H2A.Z by the SWR1 chromatin-remodeling complex is critical for the appropriate expression of many genes in eukaryotes, yet, despite its importance, the composition of the Arabidopsis SWR1 complex has not been thoroughly analyzed. Here we have identified the interacting partners of a conserved Arabidopsis SWR1 subunit, actin-related protein 6 (ARP6). We isolated 9 predicted components, identifying subunits implicated in histone acetylation and interacting partners implicated in chromatin biology. We found that the methyl-CpG-binding domain 9 (MBD9) subunit functioned synergistically with ARP6 to control flowering time. MBD9, in combination with ARP6, was involved in the SWR1-mediated incorporation of the majority of H2A.Z. MBD6 was further required for deposition of H2A.Z at a distinct subset of loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5’ of genes containing high levels of activating histone marks. Our data suggests a model for MBD9 in recruiting the SWR1 complex to open chromatin of actively transcribing genes.
Project description:Deposition of histone variant H2A.Z by the SWR1 chromatin-remodeling complex is critical for the appropriate expression of many genes in eukaryotes, yet, despite its importance, the composition of the Arabidopsis SWR1 complex has not been thoroughly analyzed. Here we have identified the interacting partners of a conserved Arabidopsis SWR1 subunit, actin-related protein 6 (ARP6). We isolated 9 predicted components, identifying subunits implicated in histone acetylation and interacting partners implicated in chromatin biology. We found that the methyl-CpG-binding domain 9 (MBD9) subunit functioned synergistically with ARP6 to control flowering time. MBD9, in combination with ARP6, was involved in the SWR1-mediated incorporation of the majority of H2A.Z. MBD6 was further required for deposition of H2A.Z at a distinct subset of loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5’ of genes containing high levels of activating histone marks. Our data suggests a model for MBD9 in recruiting the SWR1 complex to open chromatin of actively transcribing genes.
Project description:Deposition of histone variant H2A.Z by the SWR1 chromatin-remodeling complex is critical for the appropriate expression of many genes in eukaryotes, yet, despite its importance, the composition of the Arabidopsis SWR1 complex has not been thoroughly analyzed. Here we have identified the interacting partners of a conserved Arabidopsis SWR1 subunit, actin-related protein 6 (ARP6). We isolated 9 predicted components, identifying subunits implicated in histone acetylation and interacting partners implicated in chromatin biology. We found that the methyl-CpG-binding domain 9 (MBD9) subunit functioned synergistically with ARP6 to control flowering time. MBD9, in combination with ARP6, was involved in the SWR1-mediated incorporation of the majority of H2A.Z. MBD6 was further required for deposition of H2A.Z at a distinct subset of loci. MBD9 was preferentially bound to nucleosome-depleted regions at the 5’ of genes containing high levels of activating histone marks. Our data suggests a model for MBD9 in recruiting the SWR1 complex to open chromatin of actively transcribing genes.
Project description:The chromatin of individual chromosomes is organized into chromosome territories (CTs) in the interphase nucleus. The spatial arrangement of CTs is non-random and evolutionarily conserved. The gene-dense and gene-poor CTs are positioned in the nuclear center and periphery, respectively. As candidates for key molecules involved in nuclear organization, we have investigated the nuclear actin-related proteins (Arps), which include the evolutionarily conserved actin-family together with conventional actin. We used a conditional knockout system with chicken DT40 cells to analyze the functions of the actin-related protein Arp6. Consistent with a previous identification of Arp6 in the SRCAP chromatin remodeling complex, the histone variant H2AZ was significantly decreased in the chromatin of Arp6-deficient cells. Most importantly, Arp6-deficient cells had impaired radial positioning of both gene-poor macrochromosome and gene-rich microchromosome CTs. A transcription microarray analysis of the cells suggests that the radial positioning of CTs impacts only a limited number of genes and plays an active role in repression, rather than in induction. As far as we know, this report is the first observation that an inner nuclear protein is required for the radial distribution of CTs, and will provide new insight into the mechanisms and physical significance of the positioning of CTs in the nucleus.
Project description:Background: Chromatin remodeling complexes facilitate the access of enzymes that mediate transcription, replication or repair of DNA by modulating nucleosome position and/or composition. Ino80 is the DNA-dependent Snf2-like ATPase subunit of a complex whose nucleosome remodeling activity requires actin-related proteins, Arp4, Arp5 and Arp8, as well as two RuvB-like DNA helicase subunits. Budding yeast mutants deficient for Ino80 function are not only hypersensitive to reagents that induce DNA double strand breaks, but also to those that impair replication fork progression. Results: To understand why ino80 mutants are sensitive to agents that perturb DNA replication, we used chromatin immunoprecipitation to map the binding sites of the Ino80 chromatin remodeling complex on four budding yeast chromosomes. We found that Ino80 and Arp5 binding sites coincide with origins of DNA replication and tRNA genes. In addition, Ino80 was bound at 67% of the promoters of genes that are sensitive to ino80 mutation. When replication forks were arrested near origins in the presence of hydroxyurea (HU), the presence of the Ino80 complex at stalled forks and at unfired origins increased dramatically. Importantly, the resumption of DNA replication after release from a HU block was impaired in the absence of Ino80 activity. Mutant cells accumulated double-strand breaks as they attempted to restart replication. Consistently, ino80-deficient cells, although proficient for checkpoint activation, delay recovery from the checkpoint response. Conclusions: The Ino80 chromatin remodeling complex is enriched at stalled replication forks where it promotes the resumption of replication upon recovery from fork arrest. Keywords: ChIP-chip