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Arginine-Serine (RS) domain-containing proteins are RNA binding proteins with multiple functions in RNA metabolism. In mammalian cells this group of proteins is also implicated in regulation and coordination of cell cycle and apoptosis. In trypanosomes, an early branching group within the eukaryotic lineage, this group of proteins is represented by 3 members, two of them are SR proteins and have been recently shown to be involved in rRNA processing as well as in pre-mRNA splicing and stability. Here we report our findings on the 3rd member, the SR-related protein TbRRM1. In the present study, we showed that TbRRM1 ablation by RNA-interference in T. brucei procyclic cells leads to cell-cycle block, abnormal cell elongation compatible with the nozzle phenotype and cell death by an apoptosis-like mechanism. Our results expand the role of the trypanosomal RS-domain containing proteins in key cellular processes such as cell cycle and apoptosis-like death, roles also carried out by the mammalian SR proteins, and thus suggesting a conserved function in this phylogenetically conserved protein family. [ABSTRACT FROM AUTHOR]

Trypanosoma cruzi, the agent of Chagas disease, does not seem to control gene expression through regulation of transcription initiation and makes use of post-transcriptional mechanisms. We report here a 43-nt U-rich RNA element located in the 3'-untranslated region (3'-UTR) of a large number of T. cruzi mRNAs that is important for mRNA abundance in the intracellular amastigote stage of the parasite. Whole genome scan analysis, differential display RT-PCR, Northern blot, and RT-PCR analyses were used to determine the transcript levels of more than 900 U-rich-containing mRNAs of large gene families as well as single and low copy number genes. Our results indicate that the 43-nt U-richmRNAelement is preferentially present in amastigotes. The cis-element of a protein kinase 3'-UTR but not its mutated version promoted the expression of the green fluorescent protein reporter gene in amastigotes. The regulatory ciselement, but not its mutated version, was also shown to interact with the trypanosome-specific RNA-binding protein (RBP) TcUBP1 but not with other related RBPs. Co-immunoprecipitation experiments of TcUBP1-containing ribonucleoprotein complexes formed in vivo validated the interaction with representative endogenous RNAs having the element. These results suggest that this 43-nt U-rich element together with other yet unidentified sequences might be involved in the modulation of abundance and/or translation of subsets of transcripts in the amastigote stage. [ABSTRACT FROM AUTHOR]