Linker histones tune the length and shape of chromosomes

Human life hinges on the ability of our cells to cram six feet of DNA into a 10-micron nucleus—equivalent to fitting a mile of string inside one green pea. But stuffing genes into cramped quarters is only half the battle. ...

How proteins bind 'hidden' DNA

How can proteins bind DNA in the cell nucleus, where it is present in form of chromatin, tightly wrapped around histones and therefore mostly inaccessible? Recently, several studies began to uncover the various strategies ...

Computer simulations animate in atomic detail how DNA opens

Researchers from the Hubrecht Institute in Utrecht (The Netherlands) and the Max Planck Institute for Molecular Biomedicine in Münster (Germany) used computer simulations to reveal in atomic detail how a short piece of DNA ...

Hi-CO unravels the complex packing of nucleosomes

Scientists at Kyoto University's Institute for Integrated Cell-Material Sciences (iCeMS) in Japan have developed a technology that produces high-resolution simulations of one of the basic units of our genomes, called the ...

New method to analyze nucleosomes

Northwestern Medicine scientists have developed a new method to analyze the protein composition of intact nucleosomes without losing combinatorial information present in chromatin. The technique, called Nuc-MS, could help ...

Chromatin remodelers never rest to keep our genome open

Chromatin remodelers are needed to take nucleosomes away from DNA in order to make room for transcription factors to bind, and regulate the activity of our genes. It has been unclear how dynamic this process is. Researchers ...

How dividing cells avoid setting off false virus alarms

One feature of cell division has long puzzled scientists. The nucleus briefly disappears, leaving the cell's DNA exposed. Normally, bare DNA indicates a viral infection and triggers enzymatic alarms that alert the immune ...

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Nucleosome

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.

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