Comparison of the genes coding for the common 5' terminal sequence of messenger RNAs in three trypanosome species

Messenger RNAs of Trypanosoma brucei share a common 5' terminal sequence of 35 nucleotides, encoded by a mini-exon located in 1.35-kb tandemly linked repeats. We show here that sequences, almost identical to the mini-exon of T. brucei, are present in mRNAs from members of two other kinetoplastid subgenera: Trypanosoma vivax and Trypanosoma cruzi. As in T. brucei, these mini-exons are encoded by small tandemly linked repeat elements. We have determined and compared the nucleotide sequences of the mini-exon repeats from T. brucei, T. vivax and T. cruzi. This analysis shows that the mini-exon, its immediate flanking sequences and a T-rich stretch downstream are conserved, but little else. Our data establish the generality of the novel transcription system, that was first found in T. brucei and that yields mRNAs with common, repeat-encoded, 5' termini.