C-TERMINAL AMINO ACIDS AND SEQUENCES OF CALF AND RAT THYMUS HISTONES

1. 1. In order to clarify further the complexity of the histones, the C-terminal amino acids of the five main histone fractions from calf thymus have been examined by means of hydrazinolysis, carboxypeptidases and a 3H-labelling method. 2. 2. The fractions F1, F2a2, and F2b all have lysine C-terminal residues, whereas F2a1 has a glycine and F3 and alanine C-terminal. 3. 3. The results were semi-quantitative, but the lowest weights of histone found (10 000-25 000 g) per mole of C-terminal residue were near the molecular weights given by other methods. 4. 4. The release of amino acids by carboxypeptidases suggested that the C-terminal sequence in histone F1 is -Lys-Ala-Lys; in F2a2, Val-Gly-Ala-Arg-His Lys and in F3, -Arg-Ala. 5. 5. The five rat thymus histones were found to have the same C-terminal amino acids as the corresponding calf thymus fractions. © 1969.