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The LRS and SIN domains: two structurally equivalent but functionally distinct nucleosomal surfaces required for transcriptional silencing.

ABSTRACT: Genetic experiments have identified two structurally similar nucleosomal domains, SIN and LRS, required for transcriptional repression at genes regulated by the SWI/SNF chromatin remodeling complex or for heterochromatic gene silencing, respectively. Each of these domains consists of histone H3 and H4 L1 and L2 loops that form a DNA-binding surface at either superhelical location (SHL) +/-2.5 (LRS) or SHL +/-0.5 (SIN). Here we show that alterations in the LRS domain do not result in Sin(-) phenotypes, nor does disruption of the SIN domain lead to loss of ribosomal DNA heterochromatic gene silencing (Lrs(-) phenotype). Furthermore, whereas disruption of the SIN domain eliminates intramolecular folding of nucleosomal arrays in vitro, alterations in the LRS domain have no effect on chromatin folding in vitro. In contrast to these dissimilarities, we find that the SIN and LRS domains are both required for recruitment of Sir2p and Sir4p to telomeric and silent mating type loci, suggesting that both surfaces can contribute to heterochromatin formation. Our study shows that structurally similar nucleosomal surfaces provide distinct functionalities in vivo and in vitro.

SUBMITTER: Fry CJ

PROVIDER: S-EPMC1636829 | biostudies-literature | 2006 Dec

REPOSITORIES: biostudies-literature

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The LRS and SIN domains: two structurally equivalent but functionally distinct nucleosomal surfaces required for transcriptional silencing.

Fry Christopher J CJ Norris Anne A Cosgrove Michael M Boeke Jef D JD Peterson Craig L CL

Molecular and cellular biology 20061002 23

Genetic experiments have identified two structurally similar nucleosomal domains, SIN and LRS, required for transcriptional repression at genes regulated by the SWI/SNF chromatin remodeling complex or for heterochromatic gene silencing, respectively. Each of these domains consists of histone H3 and H4 L1 and L2 loops that form a DNA-binding surface at either superhelical location (SHL) +/-2.5 (LRS) or SHL +/-0.5 (SIN). Here we show that alterations in the LRS domain do not result in Sin(-) pheno ...[more]

PMID: 17015465

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Project description:BackgroundMammalian dosage compensation is achieved by the inactivation of one X chromosome in XX individuals. In eutheria this process is initiated early in development by the long non-coding RNA XIST. Studies of the initiation of silencing by XIST have focussed on mouse models, so the domains of XIST required to induce silencing in humans, and their relationship with domains required to establish heterochromatin remain to be determined.MethodsWe have previously established an inducible XIST cDNA in somatic cells and shown it can induce silencing and recruit heterochromatic features. We now assess a series of deletions across the transgene for the ability to induce silencing and integrate these results with time-course and chromatin-remodelling inhibitor treatments to follow the steps of XIST-induced silencing and heterochromatinization.DiscussionWe find that in addition to the previously reported necessity of the 5' A repeat region for XIST-induced silencing, the 1 kb around the small F repeat region and a non-repetitive region at the 3' end of the RNA are also required to silence genes. Silencing of genes up to 17 Mb from the XIST integration occurs within 2 days, while formation of a Cot-1 depleted domain is slower, and more dependent on the region encompassing Repeat F. The role of this region encompassing Repeat F in both the silencing of actively transcribed genes, the spread of H3K27me3 and the formation of a transcriptionally inert domain suggests a role in a pathway crucial for the spread of XIST across the chromatin to target distal regions of inactivation. Histone deacetylation requires only the A repeat region, with HDAC3 inhibition showing limited effect on silencing, but an impact on H3K27me3 recruitment, and as a result the recruitment of MacroH2A. Global HDAC inhibition impacted silencing in both a distance and dose-dependent fashion. The E repeat region was required for CIZ1 and H4K20me1 recruitment as well as H3K27me3; however, these appeared to act relatively independently. The H3K27me3 mark established by PRC2 integrated silencing and many of the heterochromatic features, while the PRC1 mark ubH2A appeared to be downstream of silencing in these human somatic cells.

Dataset Information

The LRS and SIN domains: two structurally equivalent but functionally distinct nucleosomal surfaces required for transcriptional silencing.

Publications

The LRS and SIN domains: two structurally equivalent but functionally distinct nucleosomal surfaces required for transcriptional silencing.

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