Identification of SL addition trans-splicing acceptor sites in the internal transcribed spacer I region of pre-rRNA in Leishmania (Leishmania) amazonensis

Trypanosomatidae is a family of early branching eukaryotes harbouring a distinctive repertoire of gene expression strategies. Functional mature messenger RNA is generated via the trans-splicing and polyadenylation processing of constitutively transcribed polycistronic units. Recently, trans-splicing of pre-small subunit ribosomal RNA in the 5' external transcribed spacer region and of precursor tRNAsec have been described. Here, we used a previously validated semi-nested reverse transcription-polymerase chain reaction strategy to investigate internal transcribed spacer (ITS) I acceptor sites in total RNA from Leishmania (Leishmania) amazonensis. Two distinct spliced leader-containing RNAs were detected indicating that trans-splicing reactions occur at two AG acceptor sites mapped in this ITS region. These data provide further evidence of the wide spectrum of RNA molecules that act as trans-splicing acceptors in trypanosomatids.

Footprints of a trypanosomatid RNA world: pre-small subunit rRNA processing by spliced leader addition trans-splicing

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.

Efficient Depletion of Multiple SARS-CoV mRNAs by a Single Small Interfering RNA Targeting The Leader Sequence / 生物化学与生物物理进展

Small interfering RNAs (siRNAs) can efficiently inhibit gene expression by sequence-specific RNA interference (RNAi). A common 5' leader sequence exists in the genomic RNA and all subgenomic RNAs of SARS-CoV, and is well conserved among various SARS-CoV strains, thus providing a preferable target for RNAi of SARS-CoV replication. Here efficient depletion of the SARS-CoV mRNAs by either a synthetic siRNA or DNA vector-derived short hairpin RNAs (shRNAs) targeting the leader sequence in mammalian cell lines were reported. The siRNA or shRNAs efficiently suppressed the expression of an EGFP reporter gene which contains the leader sequence at the 5' end. Both the siRNA and shRNAs efficiently knocked down the levels of leader-containing transcripts of three SARS-CoV genes encoding the spike protein, membrane protein and nucleocapsid protein were demonstrated. The results suggest that RNAi targeting the leader sequence is a potential efficient strategy for anti-SARS-CoV therapy.

Screening of cDNA Clone for Putative RNA Polymerase Subunit of Cysticercus cellulosae / 中国寄生虫学与寄生虫病杂志

Objective To obtain related genes of Cysticercus cellulosae from spliced leader (SL) cDNA library. Methods Spliced leader library of Cysticercus cellulosae was constructed using SL specific primer and oligo (dT)15 with M13M4 primer, and positive clones were then screened randomly, identified with enzyme restriction, followed by sequencing and homologous analysis. Results The amino acid sequence, encoded by the positive clone with a poly (A) 22 tail and a complete open reading frame (ORF), was with homology of RNA polymerase subunit genes of human, B. napus, fission yeast, A. thaliana, C. elegans and fruit fly up to 71.6%. Conclusion The protein, RNA polymerase subunit encoded putatively by the clone, is high conservative in different species.