Extension of the Amino Acid Sequence of a Lysine-rich Histone

The amino acid sequence of a lysine-rich histone from rabbit thymus has been extended from residue 72 to residue 107. This region is rich in hydrophobic residues, poor in basic residues, and lacks proline. There is a region of at least 67 consecutive residues in the histone that contains no proline. The data establish that a previously reported phosphorylation site in calf thymus lysine-rich histone corresponds to residue 105 in the rabbit thymus histone sequenced. Two of the phosphorylation sites of lysine-rich histone have thus been shown to lie at the extremities of the region rich in hydrophobic residues and devoid of prolines. Additional tryptic peptides were isolated which together seem to account for the remaining half of the molecule.