Studies on nuclear proteins. I. Observations on the tissue and species specificity of the moderately lysine-rich histone fraction 2b.

Abstract

Abstract 1. 1. Species and tissue specificity of the moderately lysine-rich histone Fraction 2b (F2b) was studied. This fraction was prepared from calf thymus, rat spleen and thymus, Walker carcinosarcoma 256, and from chicken erythrocytes. The purified F2b histones were analyzed; the NH 2 -terminal amino acid was proline, lthe C-terminal amino acid was lysine. The F2b histones are relatively rich in lysine (14.5–15.5%), alanine (10.3–10.8%), and in serine (9.1–9.5%). A characteristic feature of the F2b histones is the nearly equal content of leucine and isoleucine. Other histone fractions reported in the literature have significantly more leucine than isoleucine. 2. 2. The F2b histones were digested with trypsin and the resulting peptides were resolved by paper chromatography and electrophoresis (fingerprinting). Peptide patterns obtained for various tissues were practically identical. Selected tryptic peptides were isolated and analyzed. Comparison of the amino acid composition of corresponding peptides from calf thymus and Walker carcinosarcoma also failed to reveal any tissues or species specificity of the F2b histones in these two tissues. 3. 3. The kinetics of the amino acid release from the C-terminus of teh F2b histones by carboxypeptidases A and B (EC 3.4.2.1 and EC 3.4.2.2) were remarkably similar for histones from various tissues, indicating no species specificity of the C-terminal sequence of amino acids in this fraction. 4. 4. It was concluded that the differences between the primary structure of F2b histones from different tissues are small or negligible and it was suggested that the genetic information coding for these proteins must be very stable, possibly a part of the primordial genome.