Immunochemical Specificity in Lysine-rich Histone Subfractions

Antibodies to purified calf thymus F1, and to chromatographically purified subfractions of calf thymus F1 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 F1 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 F1 from either calf thymus or calf liver, but anti-Subfraction III serum reacted much more strongly with the thymus F1 than with the liver F1. Thus qualitative differences occur in the Subfraction III components from these two organs in one species. All sera reacted more effectively with calf thymus F1 than with rat thymus or mouse spleen F1. Chromatographically separated Subfractions I to V of rat thymus F1 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 g II g IV >> I, V; with anti calf thymus Subfraction II serum: II g IV >> I, III, V; with anti calf thymus Subfraction III serum: II g I g III >> IV, V. The immunological data suggest that the variability among the F1 histones is greater than has been assumed on the basis of chromatographic and electrophoretic analyses.