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 hyper variable regions expressed preferentially in vertebrate associated stages o f the parasite. In this work, a novel mucin-type gene family is reported, c omposed of two groups of genes organized in independent tandems and having very short open reading frames, The structures of deduced proteins share th e N and C termini but differ in central regions. One group has repeats with the consensus Lys-Asn-Thr(7)-Ser-Thr(3)-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'-untr anslated region, The highest mRNA level for S and L groups are in the epima stigote stage but they show distinct developmentally regulated patterns. Tr anscripts are short lived and their steady-state abundance is regulated pos t-transcriptionally with increased mRNA stability in insect stage epimastig ote. AU-rich sequences, similar to ARE motives known to cause mRMA instabil ity in higher eukaryotes, are present in the 3'-untranslated region of the transcripts. In transfection experiments this sequence is shown to be funct ional for the L group destabilizing its mRNA in a stage-specific manner. Fu rthermore, an effect of this AU-rich region on translation efficiency is sh own, To our knowledge, this is the first time that a functional ARE sequenc e-dependent post-transcriptional regulation mechanism is reported in a lowe r eukaryote.