H44 HIST4H4 [ edit ] Structure The nucleosome core is formed of two H2A-H2B dimers and a H3-H4 tetramer, forming two nearly symmetrical halves by tertiary structure ( C2 symmetry; one macromolecule is the mirror image of the other). [ 6 ] The H2A-H2B dimers and H3-H4 tetramer also show pseudodyad symmetry.