title: Accessibility of tyrosyl residues altered by formation of the histone 2A/2B complex.
abstract: The availability of tyrosyl residues to surface iodination was analyzed for histone 2A (H2A), histone 2B (H2B), and the H2A/H2B complex. When H2A is free in solution (200 mM NaCl, pH 7.4) tyrosine-39 and one or both tyrosines-50 and -57 were readily iodinated. Tyrosines-83 and -121 of H2B were iodinated, both when the histone was free in solution and when it was associated with H2A, while tyrosines-37, -40, and -42 of H2B were not iodinated under either condition. When H2A and H2B were associated or covalently cross-linked, all tyrosyl residues of H2A were unavailable for iodination. We also found that the iodination of nondenatured H2A and H2B did not inhibit formation of the H2A/H2B complex. These results indicate that the amino-terminal regions of the hydrophobic portions of H2A and H2B undergo significant conformational changes upon formation of the H2A/H2B complex. These conformational shifts occur in the same region of the H2A/H2B complex that contains a contact site between H2A and H2B in the nucleosome, thus indicating an involvement of this region in chromatin assembly.
mesh_terms: D000818:Animals; D002417:Cattle; D002843:Chromatin / Q000032:analysis; D006657:Histones; D007457:Iodine Radioisotopes; D046911:Macromolecular Substances; D010446:Peptide Fragments / Q000032:analysis; D011487:Protein Conformation; D014357:Trypsin; D014443:Tyrosine / Q000032:analysis*
chemical_list: D002843:Chromatin; D006657:Histones; D007457:Iodine Radioisotopes; D046911:Macromolecular Substances; D010446:Peptide Fragments; D014443:Tyrosine; D014357:Trypsin