Any of the basic proteins confined to the nuclei of eukaryotic cells. Their basic properties are due to a high proportion of the basic amino acids lysine and arginine. These properties enable them to interact very strongly with DNA. There are five types of histones: H1, H2b, H2a, H3, and H4. Two molecules of each type (except H1) aggregate together to form 7-10nm nodules around which DNA winds. H1 appears to clamp DNA into position on the nodules. Each entire DNA-histone complex is called a *nucleosome
. In forming nucleosomes, histones contribute to the packaging of relatively long DNA molecules into relatively minute chromosomes. Additionally, messenger RNA transcription only appears to be possible when H1 is released from the nucleosome. Histones may thus also play a role in the regulation of gene action. Histones are not associated with the genetic material of prokaryotes.