Mining Proteomic Databases of a Model Plant Medicago truncatula for Mosaic Proteins and Other Unconventional Translation Products

How many different proteins can be produced from a single spliced transcript? Genome annotation projects do not consider the coding potential of reading frames other than that of the reference open reading frames (refORFs). Recently, alternative open reading frames (altORFs) and their translational products, alternative proteins (altProts), have been shown to carry out important functions in various organisms. Overlapping altORFs may be involved in one fundamental mechanism so far overlooked. A few years ago, it was proposed that altORFs may act as building blocks for chimeric (mosaic) polypeptides, which are produced via multiple ribosomal frameshifting events from a single mature transcript. We adopt terminology from that earlier discussion and call this mechanism mosaic translation. This way of extracting and combining genetic information may significantly increase proteome diversity. Thus, we hypothesize that this mechanism may have contributed to the flexibility and adaptability of organisms to a variety of environmental conditions. The idea of mosaic translation is a testable hypothesis, although its direct demonstration is technically very challenging. If confirmed, this concept will revolutionize modern genetics. In this project, we would like to follow a unique strategy for the detection of mosaic proteins in proteomic databases publicly available for a very important model plant Medicago truncatula. The proposed analysis will be based on our own preliminary data already generated in the course of an ongoing TÜBİTAK1002 project. Regardless of whether the evidence for mosaic translation is found in this study, this effort will help identify such proteins later when more proteomic data become available. Finally, our approach can reveal unconventional frameshifting products that derive from the omission of several nucleotides by ribosomes (for example, +2 to +16 frameshifts). Regardless of whether such frameshifted products are parts of mosaic proteins, the potential for their detection makes this project very novel, because frameshifts longer than one nucleotide in the forward direction have not been described so far.