THE HISTONE FOLD - A UBIQUITOUS ARCHITECTURAL MOTIF UTILIZED IN DNA COMPACTION AND PROTEIN DIMERIZATION

The histones of all eukaryotes show only a low degree of primary struc ture homology, but our earlier crystallographic results defined a thre e-dimensional structural motif, the histone fold, common to all core h istones, We now examine the specific architectural patterns within the fold and analyze the nature of the amino acid residues within its fun ctional segments. The histone fold emerges as a fundamental protein di merization motif while the differentiations of the tips of the histone dimers appear to provide the rules of core octamer assembly and the b asis for nucleosome regulation. We present evidence for the occurrence of the fold from archaebacteria to mammals and propose the use of thi s structural motif to define a distinct family of proteins, the histon e fold superfamily. It appears that evolution has conserved the confor mation of the fold even through variations in primary structure and am ong proteins with various functional roles.