Histones and Metal-Binding Domains

Jeremy M. Berg (1) describes potential metal-binding domains in nucleic acid-binding proteins. These metal-binding domains consist of sequences Cys-X_(2-4)-Cys-X_(4-15)-His-X_(2-8)-Cys. Berg also cites the fact that proteins known to bind ions have short sequences of the form Cys-X_(2-4)-Cys, Cys-X_(2-4)-His, or His-X_(2-3)-His. A well-known DNA-binding protein, histone H3, also has the conserved sequence Cys-Ala-Ile-His from residues 110 to 113 (2). The nucleosome octamer has two histones of each kind of four histones. These histones are organized about an axis of symmetry, such that these conserved sequences on each histone H3 oppose each other (3). The apposition of these two histone H3 sequences would generate a structure potentially able to coordinate a metal ion, namely 2(Cys-Ala-Ile-His).