Nucleosome

Nucleosomes are the fundamental repeating subunits of all eukaryotic chromatin (except when packaged in sperm). They package DNA into chromosomes inside the cell nucleus and control gene expression. They are made up of DNA and four pairs of proteins called histones, and resemble "beads on a string of DNA" when observed with an electron microscope. The nucleosome hypothesis proposed by Don and Ada Olins and Roger Kornberg in 1974, was a paradigm shift for understanding eukaryotic gene expression. The proteins that make up the nucleosome are called histones. Histones H2A, H2B, H3 and H4 are part of the nucleosome while histone H1 is the linker DNA between the two nucleosomes.
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Nucleosome /nu·cleo·some/ any of the complexes of histone and DNA in eukaryotic cells, seen under the electron microscope as beadlike bodies on a [more]Nucleosome - Community and Resources

Structure responsible in part for the compactness of a chromosome. Each nucleosome consists of a sequence of DNA wrapped around a core of histone (a type of protein).

A beadlike structure of eukaryotic chromosomes. It consists of a core of eight histone molecules and a DNA segment of about 150 base pairs. Each nucleosome is separated from another by a linker DNA sequence of about 50 base pairs. Nucleosome structure helps to fold DNA into a compact form in the interphase nucleus. Otherwise the length of a chromosome, when linear, is many orders of magnitude greater than the diameter of the nucleus.