histone proteins

MOLECULAR BIOLOGY: CHROMATIN DNA PACKAGING AND GENE SILENCING: "The DNA of eukaryotic genomes is packaged in nucleosomes, with approximately 167 base pairs (bp) of DNA wrapped in two left-handed turns around a core of eight histones (an [H3 4]2 tetramer and two dimers of [H2A H2B]). Histone H1 binds to the DNA where the DNA enters and exits from association with the core. 'Linker' DNA of approximately 10-50 bp extends to the next histone core. The carboxy-terminal two thirds of the core histones establish the very stable interactions that create the octamer and bind DNA to its surface, whereas the amino-terminal tails are available for interaction with other chromosomal components. The tails are substrates for a number of enzymes that modify specific amino acids of specific histones."