AU-rich elements in the 3'-untranslated region of a new mucin-type gene family of Trypanosoma cruzi confers mRNA instability and modulates translation efficiency

Trypanosoma cruzi has a complex mucin gene family of 500 members with hypervariable regions expressed preferentially in vertebrate associated stages of the parasite. In this work, a novel mucin-type gene family is reported, composed of two groups of genes organized in independent tandems and having very short open reading frames. The structures of deduced proteins share the N and C termini but differ in central regions. One group has repeats with the consensus Lys-Asn-Thr⁷-Ser-Thr³-Ser(Ser/Lys)-Ala-Pro and the other a Thr-rich sequence of the type Asp-Gln-Thr^17-20-Asn-Ala-Pro- Ala-Lys-Asp-Thr^5-7-Asn-Ala-Pro-Ala-Lys. In both cases, expected mature core proteins are around 7 kDa. Both groups, named L and S, respectively, differ in the structure of genomic loci and mRNA, with differential blocks in the 3'-untranslated region. The highest mRNA level for S and L groups are in the epimastigote stage but they show distinct developmentally regulated patterns. Transcripts are short lived and their steady-state abundance is regulated post-transcriptionally with increased mRNA stability in insect stage epimastigote. AU-rich sequences, similar to ARE motives known to cause mRNA instability in higher eukaryotes, are present in the 3'-untranslated region of the transcripts. In transfection experiments this sequence is shown to be functional for the L group destabilizing its mRNA in a stage-specific manner. Furthermore, an effect of this AU-rich region on translation efficiency is shown. To our knowledge, this is the first time that a functional ARE sequence-dependent post-transcriptional regulation mechanism is reported in a lower eukaryote.