Memórias do Instituto Oswaldo Cruz
Print version ISSN 0074-0276
MAYER, Mario Gustavo; SANTOS, Marcos Gonzaga dos; SILVA, Maria Fernanda Laranjeira da and FLOETER-WINTER, Lucile Maria. Footprints of a trypanosomatid RNA world: pre-small subunit rRNA processing by spliced leader addition trans-splicing. Mem. Inst. Oswaldo Cruz [online]. 2012, vol.107, n.4, pp. 522-531. ISSN 0074-0276. http://dx.doi.org/10.1590/S0074-02762012000400013.
The addition of a capped mini-exon [spliced leader (SL)] through trans-splicing is essential for the maturation of RNA polymerase (pol) II-transcribed polycistronic pre-mRNAs in all members of the Trypanosomatidae family. This process is an inter-molecular splicing reaction that follows the same basic rules of cis-splicing reactions. In this study, we demonstrated that mini-exons were added to precursor ribosomal RNA (pre-rRNA) are transcribed by RNA pol I, including the 5' external transcribed spacer (ETS) region. Additionally, we detected the SL-5'ETS molecule using three distinct methods and located the acceptor site between two known 5'ETS rRNA processing sites (A' and A1) in four different trypanosomatids. Moreover, we detected a polyadenylated 5'ETS upstream of the trans-splicing acceptor site, which also occurs in pre-mRNA trans-splicing. After treatment with an indirect trans-splicing inhibitor (sinefungin), we observed SL-5'ETS decay. However, treatment with 5-fluorouracil (a precursor of RNA synthesis that inhibits the degradation of pre-rRNA) led to the accumulation of SL-5'ETS, suggesting that the molecule may play a role in rRNA degradation. The detection of trans-splicing in these molecules may indicate broad RNA-joining properties, regardless of the polymerase used for transcription.
Keywords : external transcribed spacer; spliced leader RNA; RNA polymerase I -spliceosome; RNA polymerase II carboxy-terminal domain.