CLONING, CHARACTERIZATION AND EXPRESSION OF THE GENE THAT ENCODES THEMAJOR NEUTRALIZATION-SPECIFIC ANTIGEN OF AFRICAN HORSESICKNESS VIRUS SEROTYPE-3

The gene encoding the outer capsid protein, VP2, of African horsesickn ess virus serotype 3 (AHSV-3) has been sequenced in its entirety from cDNA clones of the segment 2 RNA, and compared with the previously pub lished VP2 gene sequence of AHSV-4. AHSV-3 genome segment 2 was shown to be 3221 nucleotides in length, encoding a protein of 1057 amino aci ds with a 50.5 % identity to the amino acid sequence of AHSV-4 VP2. Tw o areas of high variability (approximately 35 % identity) were identif ied. The N-proximal variable region (amino acids 128 to 309) exhibited significant hydrophilicity, suggesting a possible role in the determi nation of the serotype-specific immune response. VP2 of AHSV-3 has fur thermore been expressed in a baculovirus expression system. The expres sed protein was shown to react specifically with an anti-AHSV-3 serum in Western blots. Antibodies raised in rabbits and guinea-pigs against the recombinant VP2 neutralized the virus in a plaque reduction assay , confirming the identity of VP2 as the major neutralization-specific antigen of AHSV.