Regulation of Expression for the RNP-4F Splicing Assembly Factor in the Fruit-Fly Drosophila melanogaster

Intron splicing in eukaryotic organisms requires the interactions of five snRNAs and numerous different proteins in the spliceosome. Although the molecular mechanism behind splicing has been well studied, relatively little is known about regulation of expression for these splicing factor proteins. One of these proteins is the evolutionarily-conserved Drosophila RNP-4F splicing assembly factor. This protein is transcribed from a single gene into two developmentally regulated mRNAs that differ in their 5’-UTR structure. In the longer isoform, known to be abundant in the developing fly central nervous system, a conserved retained intron which folds into a stem-loop has been implicated in expression control of the mRNA. Here, we describe construction and utilization of several new rnp-4f gene expression study vectors using a GFP reporter in the ΦC31 system. The results confirm our previous observation that presence of the regulatory stem-loop enhances RNP-4F protein expression. However, in that study, the enhancement factor protein was not identified. We show here that overexpression of the RNP-4F transgene compared to the control results in additional translation, as indicated by the GFP reporter in the fluorescent images. These results are interpreted to show that RNP-4F protein acts back on its own mRNA 5’-UTR regulatory region via a feedback pathway to enhance protein synthesis in the developing fly central nervous system. A model is proposed to explain the molecular mechanism behind rnp-4f gene expression control.