Structural aspects of histone complexes and nucleosomes revealed by the accessibility of cysteine side chains.
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. The kinetic approach described in the present work provides a highly sensitive means to probe the homogeneity of H3 containing protein complexes.
D000818:Animals; D002417:Cattle; D002645:Chickens; D002843:Chromatin / Q000648:ultrastructure*; D003545:Cysteine; D004247:DNA / Q000097:blood; D004228:Dithionitrobenzoic Acid; D004912:Erythrocytes; D006657:Histones / Q000097:blood; D009994:Osmolar Concentration; D011487:Protein Conformation; D013950:Thymus Gland
D002843:Chromatin; D006657:Histones; D004247:DNA; D004228:Dithionitrobenzoic Acid; D003545:Cysteine