Abstract
Two new histones have been found in sexually mature testes of several mammals. The new histones have been identified as a new F1 (TF1) and F2b (TF2b) on the basis of their behavior upon chemical fractionation procedures and electrophoresis at several urea concentrations. The new testis-specific histones are absent in very immature animals and in somatic tissues. However, by day 20, in the rat, the histone pattern is that of the adult, displaying nearly a full complement of TF1 and TF2b. The new histone complement evidently is characteristic of prespermatid germ cells. The degree of evolutionary variations in these histones and in other basic sperm proteins, as detected by change in electrophoretic mobility, appears to be much greater than that seen in somatic histones.