Proton Magnetic Resonance Studies of the Interactions of Histones F1 and F2B with DNA

Abstract

THE determination of sequences of histones F2A1(refs. 1 and 2) and F2B (ref. 3) and the amino-acid compositions of peptides of histone F1 (ref. 4) has shown that the distribution of residues along the polypeptide chains is extremely irregular. In particular, different regions of the molecule have markedly different characters. Thus the amino half of F2A1 has a ratio of basic to acidic residues of 15.6: 1 while for the carboxyl half of the molecule it is 1.5 : 1; for F2B this ratio is 13 : 1 for the amino quarter of the molecule and 1.9: 1 for the remainder. In the case of F1 this “polarity” is reversed: the carboxyl half of the molecule has a ratio of basic to acidic residues of 15 : 1, the amino half of 1.2 : 1. Further, regions rich in basic residues also contain a high proportion of helix destabilizing residues, proline in F1 and F2B and glycine in F2A1. In contrast, the non-basic regions contain a higher proportion of the apolar residues regarded as helix stabilizers, and higher proportions of acidics, aromatics and threonine and serine residues. The characterization of two different regions led to the suggestion^1–4 that the basic regions of the polypeptide chains are the primary sites of interaction with DNA, while the non-basic regions have the potential for the formation of definite conformations and might be involved in specific interactions other than with DNA.