The determination of the primary structure of histones F3 from chicken erythrocytes by automatic Edman degradation. 1. Cleavage and alignment of fragments.

Abstract

In order to determine the sequence of histone F3 by automatic Edman degradation, this protein was fragmented into a series of smaller fragments. Specific chemical cleavages rather than enzymatic degradations were applied in such a way as to yield a limited number of larger fragments.In the first step the histone F3 dimer was cleaved at the two methionine residues with cyanogen bromide. The three fragments were separated and purified by gel filtration. Their respective sizes were 90, 30 and 15 amino‐acid residues.The two larger fragments were both cleaved with N‐bromosuccinimide at tyrosine residues. They in turn yielded three and two fragments, respectively, which could be readily purified by gel filtration and carboxymethyl‐cellulose ion‐exchange chromatography.One of the larger fragments obtained by cleaving the 90 residue fragment at its tyrosine residues was further degraded by dilute acid into another three fragments and two free aspartic acid residues which also could be purified by gel filtration.The position of all the 10 fragments in the protein molecule became apparent by comparing the N‐ and C‐terminal amino‐acid residues of the starting material and the cleaved products after each cleavage.The simplicity of the peptide mixture after each cleavage resulted in an easy separation of the fragments.