Conservative Amino‐Acid Replacement in the Tyrosine Region of the Lysine‐Rich Histones

A comparison has been made of the sequence of the tyrosine‐containing tryptic peptide derived from the purified, unfractionated, lysine‐rich histone complement of the calf thymus, rat thymus and calf liver. Two tyrosine‐containing peptides, one of which is a fragment of the other, have been obtained from each tissue. The major tyrosine‐containing peptide was isolated by a single electrophoretic step in about a 50%, yield. The results indicate that the sequence of amino acids around the single tyrosine present in the lysine‐rich molecule is constant from tissue to tissue. However, this sequence varies among the molecular species comprising the lysine‐rich histone complement of a single tissue. Within a tissue, a conservative amino acid replacement in the residue penultimate to tyrosine (from the amino terminus) has been detected. The sequence of the tyrosine‐containing region was found to be Lys‐Ala‐Leu‐Ala‐ Ala Gly ‐Gly‐Tyr‐Asp‐Val‐Glu‐Lys.