The Effect of RNA Tertiary Structure on Trans-Splicing of the mod(mdg4) Gene in Drosophila melanogaster

Trans-splicing is a rare variant of the splicing process, wherein exons are joined between different pre-mRNAs. This mechanism enables the formation of a broad spectrum of mRNAs encoded by a single locus. The most prominent example in Drosophila melanogaster is the mod(mdg4) locus, where trans-splicing results in the production of more than 30 mRNAs encoding protein isoforms with distinct C-terminal domains. Previous studies have demonstrated that sequences in the 5'-region of the fourth intron of the mod(mdg4) locus play a pivotal role in initiating trans-splicing. In the present study, we show that the integration of MS2 repeats, which form a stable secondary RNA structure, into the sequence of the fourth intron completely suppressed trans-splicing. Conversely, the insertion of MS2 repeats immediately upstream of the intron only marginally reduced the efficiency of this process. Modifications of the sequences of the fourth intron that induce the formation of an additional stem loop in the pre-mRNA also negatively impacted trans-splicing. These findings underscore the significant role of RNA secondary structures in regulating trans-splicing.