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Nucleosome sliding is one of the possible mechanism for large scale tissue specific expression of genes. The transcription start site for genes expressed in a particular tissue, are nucleosome depleted while, the same set of genes in other tissue where they are not expressed, are nucleosome bound.
The nucleosome is the basic unit of DNA condensation and consists of a DNA double helix bound to an octamer of core histones (2 dimers of H2A and H2B, and an H3/H4 tetramer). About 147 base pairs of DNA coil around 1 octamer, and ~20 base pairs are sequestered by the addition of the linker histone (H1), and various length of "linker" DNA (~0 ...
One way in which this individuality occurs is through changes in genome architecture, which can alter the expression of different sets of genes. [5] These alterations can have a downstream effect on cellular functions such as cell cycle facilitation, DNA replication , nuclear transport , and alteration of nuclear structure.
Steps in nucleosome assembly. The nucleosome core is formed of two H2A-H2B dimers and a H3-H4 tetramer, forming two nearly symmetrical halves by tertiary structure (C2 symmetry; one macromolecule is the mirror image of the other). [8] The H2A-H2B dimers and H3-H4 tetramer also show pseudodyad symmetry.
[5] [12] If a region of DNA is bound by the nucleosome core (i.e. histones) or other chromatin-bound proteins (e.g. transcription factors), then MNase is unable to bind and cleave the DNA. Nucleosomes or the DNA-protein complexes can be purified from the sample and the bound DNA can be subsequently purified via gel electrophoresis and extraction.
The nucleosome assembles when DNA wraps around the histone octamer, two H2A-H2B dimers bound to an H3-H4 tetramer. The nucleosome core particle is the most basic form of DNA compaction in eukaryotes. Nucleosomes consist of a histone octamer surrounded by 146 base pairs of DNA wrapped in a superhelical manner. [10]
DNA footprinting is a method aimed at identifying protein-bound DNA. It uses labeling and fragmentation coupled to gel electrophoresis to identify areas of the genome that have been bound by proteins. [45] MNase-seq (Micrococcal Nuclease sequencing) uses the micrococcal nuclease enzyme to identify nucleosome positioning throughout the genome ...
Linker DNA connects to histone H1 and histone H1 sits on the nucleosome core. Nucleosome is technically the consolidation of a nucleosome core and one adjacent linker DNA; however, the term nucleosome is used freely for solely the core. Linker DNA may be degraded by endonucleases. [1]