Structural Aspects of Histone Complexes and Nucleosomes Revealed by the Accessibility of Cysteine Side Chains

Open Access
Publisher Website
Google Scholar
Abstract
Chemical modification with 5,5''-dithiobis-(2-nitrobenzoic acid) shows that histone H3 cysteines 110 (chicken) or 96 and 110 (calf) are completely protected in native chromatin and core particles but become unmasked simultaneously during a salt-induced dissociation. In whole histone extracted from chicken erythrocyte chromatin, H3 Cys-110 residues experience a uniform environment at 2 M NaCl and pH 5.5. In whole histone extracted under the same conditions from calf thymus, H3 Cys-96 provides a more accessible thiol group than Cys-110. At higher pH values a conformational heterogeneity is induced, causing a partial exposure of both cysteine side chains. This kinetic approach described provides a highly sensitive method to probe the homogeneity of H3-containing protein complexes.