Subcellular Localization of Fad1p in : A Choice at Post-Transcriptional Level?

FAD synthase is the last enzyme in the pathway that converts riboflavin into FAD. In , the gene encoding for FAD synthase is , from which a sole protein product (Fad1p) is expected to be generated. In this work, we showed that a natural Fad1p exists in yeast mitochondria and that, in its recombinant form, the protein is able, per se, to both enter mitochondria and to be destined to cytosol. Thus, we propose that generates two echoforms-that is, two identical proteins addressed to different subcellular compartments. To shed light on the mechanism underlying the subcellular destination of Fad1p, the 3' region of mRNA was analyzed by 3'RACE experiments, which revealed the existence of (at least) two transcripts with different 3'UTRs, the short one being 128 bp and the long one being 759 bp. Bioinformatic analysis on these 3'UTRs allowed us to predict the existence of a -acting mitochondrial localization motif, present in both the transcripts and, presumably, involved in protein targeting based on the 3'UTR context. Here, we propose that the long transcript might be responsible for the generation of mitochondrial Fad1p echoform.