The amino acid sequences of four major
capsid proteins of African horse sickness virus (serotype 4, AHSV-4) have been compared with those of Bluetongue virus of sheep. Epizootic hemorrhagic disease virus of deer, and the phylogenetic relationships established. Complete nucleotide sequence analysis of three
RNA segments (L2, L3, and M6) of AHSV-4 and their encoded products, VP2, VP3, and VP5, together with previously published data for VP7 (Roy et al., 1991), have revealed that of the four
capsid proteins the innermost
protein, VP3, is the most conserved, and the outermost
protein, VP2, is the most variable. Some 57-58% of the aligned BTV-10 and EHDV-1 VP3
amino acids are identical with those of AHSV-4. This compares to an identity of 79% between the BTV and EHDV VP3 sequences. For the VP7
proteins 64% of the aligned
amino acids are identical between BTV-10 and EHDV-1, while they share 44-46%
amino acid residues with the aligned VP7
protein of AHSV-4. By contrast, the VP2
proteins of the three viruses share only 19-24% identical
amino acids. Various other comparative analyses of the
proteins indicate that the VP2 species of the three orbiviruses are similar. Unlike VP2, the other outer
capsid protein, VP5 is more conserved among the three viruses. On alignment, the VP5 of AHSV-4 has some 43-45% identical
amino acids with that of BTV-10 and EHDV-1. Between BTV and EHDV, 62% of the aligned sequences are identical.