The hydrophobicity profile of different NS4 proteins was analysed using the Kyte and Doolittle hydrophobicity plot with a window size of 11 amino acids (aa) [22] . Sequence relatedness to proteins in public databases was assessed using the NCBI's BLAST (http://blast.ncbi.nlm.nih.gov/Blast.cgi)) and the pfam software (http://pfam.sanger.ac.uk/search/sequence). Amino acid alignments of NS4 of various orbiviruses were generated using the Clustal X program [23] and pairwise aa identities calculated using the MEGA 4 package [24] . The presence of 'coiled-coils' was indicated by analyses using the program 'COILS' (http://www.ch. embnet.org/cgi-bin/COILS_form_parser) and the PredictProtein server (http://www.predictprotein.org). The presence of nuclear localisation signals were analysed by PredictNSL, implemented in the PredictProtein server, and the cNLS Mapper (http://nlsmapper.iab.keio.ac.jp/cgi-bin/NLS_Mapper_form.cgi). Synonymous site conservation within the BTV VP6 coding sequence was analysed as described previously [25] . For this procedure, alignment columns in which the reference sequence (GenBank accession number: NC_006008) contained gap characters were removed so that the plots are in reference sequence coordinates.