25 Why no group II introns in nuclear genomes? translational repression, RNA-RNA interactions and mis-compartmentalization of mRNAs

Group II introns are commonly believed to be the progenitors of spliceosomal introns. However, the notable absence of group II introns from nuclear genomes begs examination. We have shown that although nuclear expression of a group II intron-containing pre-mRNA in yeast results in efficient transcription and protein-dependent splicing, RNA transcripts suffer nonsense-mediated decay and translational repression (Chalamcharla et al. 2010). To demonstrate the possible mechanism for the translational repression, we have investigated cellular dynamics of group II intron-containing RNAs, from transcription to cellular localization, by utilizing multi-disciplinary techniques. Specialized 5’-RACE indicates that group II intron-containing RNA and its spliced product are both 5’-capped and 3’-polyadenylated and are most eukaryotic RNA polymerase II transcripts. Additionally, primer extension assay showed that RNA transcription and splicing both initiate from the correct sites. Importantly, molecular pull-down exper...