Histone H3 is a core subunit of the eukaryotic nucleosome complex. Histones are basic nuclear proteins responsible for the nucleosome structure of chromatin. Repeating nucleosome units contain two molecules each of Histones H2A, H2B, H3, and H4 that form an octamer complex around which approximately 146 base pairs of DNA is wrapped. Linker Histone H1 interacts with DNA between nucleosome units in mediating chromatin compaction into higher order structures. (NCI) [ ]