The compaction pattern of the chromatin of trypanosomes

Protozoa of the family Trypanosomatidae are pathogenic agents of human and animal diseases. Fine structure, compaction pattern, and histone content of the soluble chromatin were investigated in procyclic forms of Trypanosoma cruzi (Chagas disease, S. America) and T. brucei brucei (Nagana disease, Africa) in comparison with rat liver chromatin. At low ionic strength chromatin was present as nucleosome filaments. Condensation into compact fibers (solenoid) was complete for rat chromatin at 100 mM salt concentration while chromatin of T. cruzi showed less condensation (tangle formation), and that of T.b. brucei did barely condense under identical experimental conditions. In general, the nucleosomes of trypanosomes, especially T.b. brucei, seemed to be less regularly arranged than those of the higher eukaryote. Addition of histone H1-containing fractions of rat liver chromatin increased the compaction of T. cruzi chromatin but had no influence on T.b. brucei chromatin. SDS-polyacrylamide gel electrophoresis revealed histone H1 and the 4 core histones in rat liver chromatin. Neither in T. cruzi nor T.b. brucei were proteins identical to rat histone H1 present. Differences existed also in molecular weight of core histones between rat and trypanosomes, as well as between T. cruzi and T.b. brucei. These differences might explain species-specific differences in the fine structural organization and compaction pattern of the chromatin of the rat, T. cruzi, and T.b. brucei.