H3F3A, which are proteins that play an essential role in maintaining genome integrity, is responsible for the nucleosome structure which are two molecules from an octamer.
It plays an essential role in maintaining genome integrity during mammalian development. Histone H3.3 is a protein that in humans is encoded by the H3F3A and H3F3B genes. Two molecules of each of the four core histones (H2A, H2B, H3, and H4) form an octamer, around which approximately 146 bp of DNA is wrapped in repeating units, called nucleosomes. Histones are basic nuclear proteins that are responsible for the nucleosome structure of the chromosomal fiber in eukaryotes. 
