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Heterochromatin,gene position effect and gene silencing   总被引:4,自引:0,他引:4  
Zhimulev IF  Beliaeva ES 《Genetika》2003,39(2):187-201
Genomes of higher eukaryotes consist of two types of chromatin: euchromatin and heterochromatin. Heterochromatin is densely packed material typically localized in telomeric and pericentric chromosome regions. Euchromatin transferred by chromosome rearrangements in the vicinity of heterochromatin is inactivated and acquires morphological properties of heterochromatin in the case of position effect variegation. One of the X chromosomes in mammal females and all paternal chromosome set in coccides become heterochromatic. The heterochromatic elements of the genome exhibit similar structural properties: genetic inactivation, compaction, late DNA replication at the S stage, and underrepresentation in somatic cells. The genetic inactivation and heterochromatin assembly are underlain by a specific genetic mechanism, silencing, which includes DNA methylation and posttranslational histone modification provided by the complex of nonhistone proteins. The state of silencing is inherited in cell generations. The same molecular mechanisms of silencing shared by all types of heterochromatic regions, be it unique or highly repetitive sequences, suggest the similar organization of these regions. No type of heterochromatin is a permanent structure as they all are formed at the strictly definite stages of early embryogenesis. Based on the bulk of evidence accumulated today, heterochromatin can be regarded as a morphological manifestation of genetic silencing.  相似文献   

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Chromatin silencing: RNA in the driving seat   总被引:3,自引:0,他引:3  
Recent studies have provided major new insights into the mechanism by which eukaryotic organisms initiate heterochromatin formation. Surprisingly, RNA appears to be a central component of the chromatin silencing machinery.  相似文献   

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Kumaran RI  Thakar R  Spector DL 《Cell》2008,132(6):929-934
The mammalian cell nucleus provides a landscape where genes are regulated through their organization and association with freely diffusing proteins and nuclear domains. In many cases, specific genes are highly dynamic, and the principles governing their movements and interchromosomal interactions are currently under intensive study. Recent investigations have implicated actin and myosin in chromatin dynamics and gene expression. Here, we discuss our current understanding of the dynamics of the interphase genome and how it impacts nuclear organization and gene activity.  相似文献   

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Chromatin structure and gene activity   总被引:12,自引:0,他引:12  
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转录后水平沉默与基因表达   总被引:8,自引:0,他引:8  
基因沉默是1个非常复杂和普遍的现象。转录后水平的基因沉默是指转基因在细胞核里能稳定转录,细胞质里却无相应的稳定态mRNA存在的现象。它往往被称为共抑制、静息作用或RNA干预等。本文介绍了转录后水平的基因沉默现象的发现、分子机理和应用等方面的进展。提出了克服转录后水平基因沉默的一些对策。  相似文献   

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The DNA sequence elements called insulators have two basic kinds of properties. Barrier elements block the propagation of heterochromatic structures into adjacent euchromatin. Enhancer blocking elements interfere with interaction between an enhancer and promoter when placed between them. We have dissected a compound insulator element found at the 5' end of the chicken β-globin locus, which possesses both activities. Barrier insulation is mediated by two kinds of DNA binding proteins: USF1/USF2, a heterodimer which recruits multiple enzyme complexes capable of marking histone on adjacent nucleosomes with 'activating' marks, and Vezf1, which protects against DNA methylation. We have found that the heterochromatic region upstream of the insulator element is maintained in its silent state by a dicer-dependent mechanism, suggesting a mechanism for Vezf1 function in the insulator. Enhancer blocking function in the β-globin insulator element is conferred by a binding site for CTCF. Consistent with this property, CTCF binding was found some years ago to be essential for imprinted expression at the Igf2/H19 locus. Work in many laboratories has since demonstrated that CTCF helps stabilize long-range interactions in the nucleus. We have recently shown that in the case of the human insulin locus such an interaction, over a distance of ~300kb, can result in stimulation of a target gene which itself is important for insulin secretion. This article is part of a Special Issue entitled: Chromatin in time and space.  相似文献   

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Generation of HIV latency during thymopoiesis   总被引:1,自引:0,他引:1  
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Chromatin structure and phaseolin gene regulation   总被引:4,自引:0,他引:4  
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