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Nucleosomes are thought to carry epigenetically inherited information in the form of covalent modifications of their core histones. Nucleosome positions in the genome are not random, and it is important to know where each nucleosome is located because this determines the accessibility of the DNA to regulatory proteins .
Euchromatin is composed of repeating subunits known as nucleosomes, reminiscent of an unfolded set of beads on a string, that are approximately 11 nm in diameter. [2] At the core of these nucleosomes are a set of four histone protein pairs: H3, H4, H2A, and H2B. [2]
In eukaryotic cells, DNA is associated with about an equal mass of histone proteins in a highly condensed nucleoprotein complex called chromatin. [14] Deoxyribonucleoproteins in this kind of complex interact to generate a multiprotein regulatory complex in which the intervening DNA is looped or wound.
This is because the histone tail domains are involved in interactions between nucleosomes. The linker histone, or H1 protein, is also involved maintaining nucleosome structure. The H1 protein has the special role of ensuring that DNA stays tightly wound. [4] Modifications to histone proteins and their DNA are classified as quaternary structure.
Examples of different levels of nuclear architecture. Nuclear organization refers to the spatial organization and dynamics of chromatin within a cell nucleus during interphase. There are many different levels and scales of nuclear organisation. At the smallest scale, DNA is packaged into units called nucleosomes, which
Histone H2A is one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells.. The other histone proteins are: H1, H2B, H3 and H4.. The crystal structure of the nucleosome core particle consisting of H2A, H2B, H3 and H4 core histones, and DNA.
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A eukaryotic cell has a nucleus that separates the processes of transcription and translation. Eukaryotic transcription occurs within the nucleus where DNA is packaged into nucleosomes and higher order chromatin structures. The complexity of the eukaryotic genome necessitates a great variety and complexity of gene expression control.