Immunochemical specificity in lysine-rich histone subfractions.

Antibodies to purified calf thymus Fl, and to chromatographically purified subfractions of calf thymus Fl histones were induced by immunization of rabbits with histone-RNA complexes. Complement fixation studies with these antibodies demonstrated structural differences between the subfractions in one organ and between those of different organs and species. The anti-F1 sera showed varying reactivity with whole Fl histone preparations from (in order of decreasing reactivity) calf thymus, lamb thymus, calf liver, rat thymus, and mouse spleen, as well as with three chromatographically separated subfractions of calf thymus. Antibodies to each of the calf thymus subfractions showed preferential reactivity with the homologous antigen and differentiated between all three components. Subfractions II and III appeared to be more closely related to each other than to Subfraction I. With anti-Subfraction I or anti-Subfraction II serum, equal reactions were observed with whole Fl from either calf thymus or calf liver, but anti-Subfraction III serum reacted much more strongly with the thymus Fl than with the liver Fl. Thus qualitative differences occur in the Subfraction III components from these two organs in one species. All sera reacted more effectively with calf thymus Fl than with rat thymus or mouse spleen Fl. Chromatographically separated Subfractions I to V of rat thymus Fl were all distinguishable from calf thymus subfractions, and immunochemical relatedness of subfractions of the two species could not be predicted from chromatographic elution positions. The order of reactivity of rat thymus subfractions was: with anti calf thymus Subfraction I serum: III > II > IV >> I, V; with anti calf thymus Subfraction II serum: II > IV >> I, III, V; with anti calf thymus Subfraction III serum: II > I > III >> IV, V. The immunological data suggest that the variability among the Fl histones is greater than has been assumed on the basis of chromatographic and electrophoretic analyses.