RNA segment 5 of broadhaven virus, a tick-borne orbivirus, shows sequence homology with segment 5 of bluetongue virus.

The sequence of Broadhaven (BRD) virus segment 5, the major genetic determinant of serotype, is 1658 nucleotides in length and contains a single open reading frame (ORF) having the coding capacity for a protein of Mr 52.5K. Comparison of the ORF of segment 5 of BRD virus with published sequences of bluetongue virus (BTV) revealed 30% nucleotide homology and 31% amino acid homology with the protein encoded by segment 5 of BTV serotype 10. Significant homology was not shown with segment 2 of BTV, the major genetic determinant of the BTV serotype. The sequences at the 3' and 5' ends determined for BRD segment 5 were similar to the respective 3' and 5' regions of BTV. The sequence data provide evidence of an evolutionary relationship between two ecologically distinct groups of orbiviruses and demonstrate changes that have occurred in the functions of genetically related genomic segments.