News tagged with nucleosomes

Discovery reveals chromosomes organize into 'yarns'

Chromosomes, the molecular basis of genetic heredity, remain enigmatic 130 years after their discovery in 1882 by Walther Flemming. New research published online in Nature by the team of Edith Heard, PhD, from the Curie Institute ...

Apr 11, 2012
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Exercise rescues mutated neural stem cells

CHARGE syndrome is a severe developmental disorder affecting multiple organs. It affects 1 in 8500 newborns worldwide. The majority of patients carry a mutation in a gene called CHD7. How this single mutation leads to the ...

Jul 05, 2013
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Researchers discover new mechanism of gene regulation

In the cells of humans and other organisms, only a subset of genes are active at any given time, depending largely on the stage of life and the particular duties of the cell. Cells use different molecular mechanisms to orchestrate ...

Feb 26, 2014
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Scientists at UCI restore long-term memory to mice

University of California-Irvine neurobiologists have discovered a protein complex in neurons that is essential to long-term memory formation and is also corrupted in the brains of people with some developmental disabilities ...

Jun 05, 2013
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Nucleosomes are the basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound around a histone protein core. This structure is often compared to thread wrapped around a spool.

Nucleosomes form the fundamental repeating units of eukaryotic chromatin, which is used to pack the large eukaryotic genomes into the nucleus while still ensuring appropriate access to it (in mammalian cells approximately 2 m of linear DNA have to be packed into a nucleus of roughly 10 µm diameter). Nucleosomes are folded through a series of successively higher order structures to eventually form a chromosome; this both compacts DNA and creates an added layer of regulatory control, which ensures correct gene expression. Nucleosomes are thought to carry epigenetically inherited information in the form of covalent modifications of their core histones. The nucleosome hypothesis was proposed by Don and Ada Olins in 1974 and Roger Kornberg.

The nucleosome core particle consists of approximately 147 base pairs of DNA wrapped in 1.67 left-handed superhelical turns around a histone octamer consisting of 2 copies each of the core histones H2A, H2B, H3, and H4. Core particles are connected by stretches of "linker DNA", which can be up to about 80 bp long. Technically, a nucleosome is defined as the core particle plus one of these linker regions; however the word is often synonymous with the core particle.

Linker histones such as H1 and its isoforms are involved in chromatin compaction and sit at the base of the nucleosome near the DNA entry and exit binding to the linker region of the DNA. Non-condensed nucleosomes without the linker histone resemble "beads on a string of DNA" under an electron microscope.

In contrast to most eukaryotic cells, mature sperm cells largely use protamines to package their genomic DNA, most likely to achieve an even higher packaging ratio. Histone equivalents and a simplified chromatin structure have also been found in Archea, proving that eukaryotes are not the only organisms that use nucleosomes.

This text uses material from Wikipedia, licensed under CC BY-SA

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