if not all, processes that require access of proteins to DNA. The basic building block of chromatin is the nucleosome, which is composed of two copies of each of four core histone proteins (H2A, H2B, H3, and H4) wrapped by 146 base pairs of DNA (Luger et al., 1997). These histone tails appear to be unstructured and are believed to participate in the formation of higher order chromatin structure by mediating internucleosomal interactions (Luger et al., 1997), as well as contact with DNA that is positioned between the nucleosomes (linker DNA) (Angelov et al., 2001).
Nishioka, K., Rice, J. C., Sarma, K., Erdjument-Bromage, H., Werner, J., Wang, Y., … Reinberg, D. (2002). PR-Set7 Is a Nucleosome-Specific Methyltransferase that Modifies Lysine 20 of Histone H4 and Is Associated with Silent Chromatin The N-terminal tails of the core histone proteins protrude. Molecular Cell, 9, 1201–1213. Retrieved from http://www.molecule.org/cgi/