Giardia lamblia Hsp90 pre‐mRNAs undergo self‐splicing to generate mature RNA in an in vitro trans‐splicing reaction

: We have previously shown that the Heat Shock Protein 90 (Hsp90) gene in G. lamblia is expressed from two ORFs localized 777 kb apart. The pre-mRNAs transcribed from these ORFs are stitched by a trans-splicing mechanism. Here, we provide mechanistic details of this process by reconstituting the reaction using in vitro synthesized pre-mRNA substrates. Using RT-PCR, northern blot and nanostring technology, we demonstrate that the in vitro synthesized pre-mRNAs have the capability to self-splice in the absence of nuclear proteins. Inhibition of the trans-splicing reaction using a ssDNA oligo corresponding to a 26-nucleotide complementary sequence confirmed their role in juxtapositioning the pre-mRNA substrates during the self-splicing reaction. Our study provides the first example of a self catalysed, trans-splicing reaction in eukaryotes.