By confocal microscopy of cells transiently transfected with pCI-NS4, we observed that NS4 localized mainly in the nucleus (Figure 2A) where it showed a strong co-localization with the nucleolar marker B23 [40] . Importantly, cells infected with either BTV-1 or BTV-8 also showed a strong nuclear co-localisation between NS4 and B23 [40] (Figure 2B ). We also observed NS4 to localise in the nucleus of the C6/36 insect cells ( Figure 2C ).