The D. melanogaster porin1 mRNA translation is regulated by its alternative 5’UTR sequences.

Voltage Dependent Anion selective channel, VDAC or porin, is a beta barrel protein located in the outer mitochondrial membrane of all eukaryotic cells [1]. In D. melanogaster, VDAC protein is coded by the porin1 gene. This gene produces two splicing variants: 1A-porin and 1B-porin. The protein is translated from the transcript 1A-porin; the alternative transcript 1B-porin, on the contrary is never translated in any tissue and in any development stage of fly [2]. Expression analysis in S. cerevisiae ∆porin1 cells showed that also in yeast the D.m. 1A-porin transcript is translated (restoring the yeast wild-type phenotype, in glycerol at 37 °C), while neither functional complementation nor any immuno-detection could be observed in cells transformed with 1B-porin. Identical results were obtained in embryonic D. melanogaster SL2 cells. In order to speculate whether the two 5′UTRs regulate the expression of other genes, SL2 cells and ∆porin1 yeast cells were transfected with gene reporters carrying upstream the ATG codon the 5′UTRs and, as hypothesized, only the 1A-transcripts were translated. To understand how the 5′UTRs are used in the regulation of D.m. porin and in the expression of gene reporters, several mutants of the 5’UTR1B were produced and used to transform yeast cells. A specific region was selected as a possible regulator of translation. RNA binding sites were detected. RNA electrophoresis mobility shift assay and RNA-pull down assay associated to mass spectrometry analysis have showed that specific translational initiation factors are able to bind the selected region, modulating the 1B-porin translation. References 1. A. Messina et al., FEBS Lett. (1996) 384:9-13 2. M. Oliva et al., Mol Genet Genomics (2002) 267:746–756.