TRYPANOSOMA-BRUCEI-BRUCEI - DIFFERENCES IN THE NUCLEAR CHROMATIN OF BLOOD-STREAM FORMS AND PROCYCLIC CULTURE FORMS

Nucleosome filaments of two stages of the life-cycle of Trypanosoma br ucei brucei, namely bloodstream forms and procyclic culture forms, wer e investigated by electron microscopy. Chromatin of bloodstream forms showed a salt-dependent condensation. The level of condensation was hi gher than that shown by chromatin from procyclic culture forms, but 30 nm fibres as formed in rat liver chromatin preparations were not foun d. Analysis of histones provided new evidence for the existence of H1- like proteins, which comigrated in the region of the core histones in SDS-PAGE and in front of the core histones in Triton acid urea gels. D ifferences were found between the H1-like proteins of the two trypanos ome stages as well as between the core histones in their amount, numbe r of bands and banding pattern. It can be concluded that T. b. brucei contains a full set of histones, including H1-like proteins, and that the poor condensation of its chromatin is not due to the absence of H1 , but most probably due to histone-DNA interaction being weak. It is o bvious that structural and functional differences of the chromatin exi st not only between T. b. brucei and higher eukaryotes, but also betwe en various stages of the life-cycle of the parasite. It is therefore n ot adequate to investigate the chromatin only of the procyclic culture forms as a model for all stages of the life-cycle of T. b. brucei.