A single-stranded DNA-binding protein shared by telomeric repeats, the variant surface glycoprotein transcription promoter and the procyclin transcription terminator of Trypanosoma brucei

In Trypanosoma brucei the genes are organised into long polycistronic trans cription units and only three promoters for protein-encoding genes and a si ngle terminator have been characterised. These promoters recruit a poll-lik e RNA polymerase for the transcription units encoding the two major stage-s pecific antigens of the parasite, the variant surface glycoprotein (VSG) of the bloodstream form and procyclin of the insect-specific procyclic form, while the terminator is that of a procyclin transcription unit, By deletion al and mutational analysis we defined the two DNA sequences essential for t he activity of the VSG promoter from a bloodstream form transcription unit and one of the functional elements of the procyclin terminator, These three short sequences are similar, and their C-rich strand binds the same protei n of 40 kDa, In addition, this factor also binds to the C-rich strand of th e telomeric repeats, the consensus target sequence being 5'-CCCTNN-3'. The factor-binding sequences are functionally interchangeable in chimeric promo ter or terminator constructs, although additional elements are required for full activity.