Therefore, the segmented genome of BTV has been thought to be monocistronic (i.e. ten genome segments encoding for 10 proteins) for almost three decades [27, 28] . Segment 9 however, contains the open reading frame (ORF) encoding VP6 but also a smaller coding sequence in the position +1 reading frame that is present in BTV and some related Orbiviruses such as African horse sickness virus and others [29] . Bioinformatic analysis predicts that the BTV ''ORFX'' encodes for a protein of 77-79 amino acid residues. This putative ORFX is subject to functional constraints at the amino acid level and its level of conservation is higher compared to that of the overlapping VP6. In addition, the ORFX putative AUG initiation codon has a strong Kozak context suggesting that this protein might be translated by leaky scanning [29] . Alternative reading frames are expressed in a variety of RNA viruses and they can play fundamental roles in viral replication and virus-host interaction. In this study, we identified a previously unknown non-structural protein and characterized its biological properties.