Corehistone

Corehistone refers to the four main histone proteins that make up the nucleosome, the basic structural unit of chromatin. These proteins are designated as H2A, H2B, H3, and H4. Together, these four core histones form an octamer, with two copies of each protein. This octamer serves as the spool around which a segment of DNA is wrapped, forming the nucleosome. This wrapping significantly compacts the DNA, allowing the large genome of eukaryotes to fit within the nucleus. The interactions between the DNA and the positively charged histone proteins are largely electrostatic, facilitated by the abundance of lysine and arginine residues in the histones. The amino-terminal tails of these core histones extend outward from the nucleosome core and are sites of extensive post-translational modifications. These modifications, such as acetylation, methylation, and phosphorylation, play a crucial role in regulating gene expression by altering chromatin structure and accessibility to transcription machinery. The precise arrangement and modification of core histones are fundamental to the organization and function of eukaryotic chromosomes.