Cloning and expression of yellowtail ascites virus segment A - Brief report

cDNA of yellowtail ascites virus (YAV) segment A encoding a polyprotein of VP2, NS, and VP3 has been cloned. Comparison of the nucleotide and the dedu ced amino acid sequences showed very high homology between YAV and other aq uatic birnaviruses. The two small open reading frames (VP5) besides the 5' terminus of the VP2 gene were found on segment A of YAV. Proteins encoded b y cDNAs from segment A and the serotype-specific epitope region on VP2 were expressed using a baculovirus vector. Western blot analysis confirmed that a polyprotein was expressed and processed into VP2 and VP3 in insect cells infected with the recombinant baculovirus containing the complete polyprot ein coding region. In the case of expression in silkworm larvae, only VP3 w as detected in hemocytes and fat body of silkworm larvae infected with the recombinant virus. The recombinant fusion protein consisting of VP2 epitope region and polyhedrin was expressed in insect cells and cross-reacted with a mouse monoclonal antibody against VP2 which had a neutralizing activity to YAV.