STAGE-SPECIFIC DIFFERENTIAL POLYADENYLATION OF MINI-EXON DERIVED RNA IN AFRICAN TRYPANOSOMES

The differentiation of African trypanosomes through several distinct s tages in their mammalian host and insect vector correlates with differ ential expression of some of the parasites' genes. In the search for g enes from Trypanosoma brucei brucei involved in switching from the act ively dividing long slender to the non-dividing short stumpy bloodstre am forms, we have isolated cDNA clones which hybridise specifically to mRNA from short stumpy forms. All clones that were characterised cont ained similar sequences. Northern blot analysis showed that: (i) RNA t ranscripts which hybridise to these clones are barely detectable in th e poly(A)+ fraction of RNA from long slender bloodstream forms and abs ent in procyclic culture forms, but are abundant in the poly(A)+ fract ion of RNA from short stumpy forms; (ii) the RNA transcripts are abund ant in the poly(A)- fraction of RNA from all life cycle stages of the trypanosomes, without significant differences and, (iii) three transcr ipts of 160, 280 and 400 nucleotides in size are detected in the poly( A)+ fraction of RNA, whereas only a single size-class of transcript of between 140 and 160 nucleotides is detectable in the poly(A)- fractio n. Sequence analysis revealed that these clones correspond to mini-exo n derived RNA containing a poly(A) tail at their 3' end. The polyadeny lation of the transcript is a post-transcriptional event since sequenc es from genomic DNA could not be amplified in the polymerase chain rea ction when mini-exon and oligo(dT) nucleotide sequences were used as p rimers. The differences in size of the transcripts detected can be acc ounted for by variations in the poly(A) tail length.