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histone octamer
A histone octamer is the eight protein complex found at the center of a nucleosome core particle. It consists of two copies of each of the four core histone proteins (H2A, H2B, H3 and H4). The octamer assembles when a tetramer, containing two copies of both H3 and H4, complexes with two H2A/H2B dimers. Each histone has both an N-terminal tail and a C-terminal histone-fold. Both of these key components interact with DNA in their own way through a series of weak interactions, including hydrogen bonds and salt bridges. These interactions keep the DNA and histone octamer loosely associated and ultimately allow the two to re-position or separate entirely.
== History of research==
Histone post-translational modifications were first identified and listed as having a potential regulatory role on the synthesis of RNA in 1964. Since then, over several decades, chromatin theory has evolved. Chromatin subunit models as well as the notion of the nucleosome were established in 1973 and 1974, respectively. Richmond and his research group has been able to elucidate the crystal structure of the histone octamer with DNA wrapped up around it at a resolution of 7 Å in 1984. The structure of the octameric core complex was revisited seven years later and a resolution of 3.1 Å was elucidated for its crystal at a high salt concentration. Though sequence similarity is low between the core histones, each of the four have a repeated element consisting of a helix-loop-helix called the histone fold motif. Furthermore, the details of protein-protein and protein-DNA interactions were fine-tuned by X-ray crystallography studies at 2.8 and 1.9 Å, respectively, in the 2000s.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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