Immunological relatedness of thymus and liver F1 histone subfracions.

Antibodies to chromatographically purified rat thymus Fl histone subfractions were induced in rabbits by immunization with histone-RNA complexes. The immunological relatedness between each of the rat thymus Fl subfractions and subfractions derived chromatographically from calf thymus and rat liver Fl was determined by quantitative microcomplement fixation. The various rat thymus peaks elicited specific antibodies; in cross-reactions with these antibodies, indices of dissimilarity between cross-reacting and homologous subfractions ranged from 1.5 to over 20. It could be calculated that some of the peaks have sequence differences as high as 20 %. None of the rat thymus subfractions corresponded immunologically to calf thymus subfractions. The highest interspecies cross-reactivity was found with antisera to rat thymus Peak II, where the indices of dissimilarity with calf thymus Peaks I to III were 4.0,2.1, and 1.6, respectively. The ranges of sequence differences between rat and calf thymus were similar to those detected between rat thymus peaks. Comparison of rat thymus and rat liver Fl subfractions reveals that the organ specificity in Fl seems to be of a lower order than the species specificity. The only definitely distinct subfraction was rat thymus Peak I. Other thymus subfractions had close homologues in the liver.