Proton Magnetic Resonance Studies of Conformational Changes in Cleaved Halves of Histone F2B

THE amino-acid sequences of the histones F2A1¹ and F2B² are of particular interest in that they have such a high degree of non-uniformity that different regions of the polypeptide chains have quite different characters. The amino-halves of the molecules have a high density of basic residues while the carboxyl-halves have far fewer basic residues and higher proportions of apolar residues and other residues which favour the formation of helical conformations. These properties have led to the suggestions that the regions of high basicity are the primary sites for interaction with DNA^1–4 in chromatin and that the non-basic regions contain any secondary structure that the molecule is capable of forming^1–4 and are the sites for histone–histone interactions^3,4. Evidence in support of this scheme has been obtained from nuclear magnetic resonance and optical spectroscopic studies of conformational changes and interactions in histones F1 and F2A1³ and F2B⁴. In these studies, however, the whole molecule has been examined and the possibility of the formation of some secondary structure in the basic region of the molecule cannot be excluded.