Histone fold

A histone fold is a structurally conserved motif found near the C-terminus in every core histone sequence in a histone octamer responsible for the binding of histones into heterodimers.

The histone fold averages about 70 amino acids and consists of three alpha helices connected by two short, unstructured loops. When not in the presence of DNA, the core histones assemble into head-to-tail intermediates (H3 and H4 first assemble into heterodimers then fuse two heterodimers to form a tetramer, while H2A and H2B form heterodimers) via extensive hydrophobic interactions between each histone fold domain in a "handshake motif".