We generated a polyclonal antiserum towards ORFX, in order to assess whether BTV expressed this previously uncharacterized protein. We detected ORFX in BSR cells infected with either BTV-8 or BTV-1 by western blotting ( Figure 1B) . Controls included BSR cells transfected with plasmids expressing ORFX either in its native form, or with eGFP fused to its C terminus. These data confirm that BTV expresses a protein encoded by an alternative reading frame located in segment 9.