THE CHROMATIN OF TRYPANOSOMES

The nuclear chromatin of trypanosomes is organised in the form of nucl eosome filaments. When soluble chromatin is prepared under suitable co nditions, a regular array of nucleosomes can be shown by electron micr oscopy. Chromatin of blood stream as well as procyclic culture forms o f Tryponosoma brucei brucei and of T. cruzi shows limited compaction a t salt concentrations increasing from 1 to 100 mM. No 30 nm fibres, ty pical for higher eukaryotes, are formed. Digestion of the nuclear chro matin with micrococcal nuclease and analysis of the histone proteins w ith various techniques reveal that the basic organisation of the trypa nosome chromatin is similar but not identical as compared to that of h igher eukaryotes. Distinct differences are present with respect to bio chemical properties of the histones as well as to their interaction wi th the DNA. The primary structure of the histones also differs signifi cantly from that found in other lower and higher eukaryotes. The funct ion of the recently described Hi-like proteins in trypanosomes is curr ently being investigated. The differences that have already been found in the structure and compaction of the trypanosome chromatin compared to that of higher eukaryotes lead us to expect differences of gene ex pression which, in turn, might offer targets for the control of trypan osomiasis.