Identification of some peptides from an arginine-rich histone and their bearing on the structure of deoxyribonucleohistone

Abstract

Arginine-rich histone from calf thymus, with alanine accounting for 85-95% of all the N-terminal groups, was digested with trypsin. A precipitate and a mixture of soluble peptides were rapidly produced. The precipitate was heterogeneous and accounted for about 25% of the histone. Amino acid analysis showed that there was one basic amino acid to every seven residues in it and the ratio of basic amino acids to acidic amino acids was only half that of the parent histone. A slightly lysine-rich histone fraction gave a precipitate accounting for 15% of the material on tryptic digestion, whereas a very lysine-rich histone fraction did not give any precipitate. The soluble peptides from the arginine-rich histone have been partially separated and characterized. Analyses showed that the spacing between the basic amino acids in that part of the histone giving the soluble peptides varied from o (juxtaposition) to 4 nonbasic residues. The structure of deoxyribonucleohistone is discussed in the light of this irregular spacing of the basic amino acids in the histone.