A New Histone from Trout Testis

A new histone has been isolated from testis cells of the rainbow trout (Salmo gairdnerii) and the initial characterization of this protein has been performed. This histone (forming about 0.5% of the total histones), was easily dissociated from purified chromatin either by chemical modification with maleic anhydride or by extraction at low salt or trichloroacetic acid concentrations. The histone was purified either by gel filtration on Bio-Gel P-10 eluted with 0.01 n HCl or by ion exchange chromatography on carboxymethylcellulose eluted with a linear gradient of lithium chloride. The molecular weight was determined to be 14,500 by the mobility of the formylated derivative during sodium dodecyl sulfateacrylamide gel electrophoresis. Dansylation revealed proline to be the amino terminus and amino acid analyses showed the complete absence of 7 amino acids including the aromatic and sulfur-containing residues. Three amino acids, lysine, alanine, and proline, accounted for 60% of the residues in the protein. Peptide maps of the tryptic peptides of the histone showed 13 unique peptides and thus ruled out an origin by degradation of one of the major histones. The new histone resembles histone I in the high content of lysine and alanine but is more similar to histone IIb2 in its molecular weight of 14,500, a prolyl N terminus, and a lysine to arginine ratio of 3:1. Pending primary structural data which should reveal whether this histone should be classified as more similar to histone I or histone IIb2, we propose to call it histone T (for trout).