MECHANISMS OF DEVELOPMENTAL REGULATION IN TRYPANOSOMA-BRUCEI - A POLYPYRIMIDINE TRACT IN THE 3'-UNTRANSLATED REGION OF A SURFACE PROTEIN MESSENGER-RNA AFFECTS RNA ABUNDANCE AND TRANSLATION

Salivarian trypanosomes are extracellular parasites of mammals that ar e transmitted by tsetse flies. The procyclic acidic repetitive protein s (PARPs) are the major surface glycoproteins of the form of Trypanoso ma brucei that replicates in the fly. The abundance of PARP mRNA and p rotein is very strongly regulated, mostly at the post-transcriptional level. The 3'-untranslated regions of two PARP genes are of similar le ngths, but are dissimilar in sequence apart from a 16mer stem-loop tha t stimulates translation and a 26mer polypyrimidine tract. Addition of either of these PARP 3'-untranslated regions immediately downstream o f a reporter gene resulted in developmental regulation mimicking that of PARP. We show that the PARP 3'-UTR reduces RNA stability and transl ation in bloodstream forms and that the 26mer polypyrimidine tract is necessary for both effects.