[Genomic structure and proteins sequence analysis of full-length of segment A of three infections bursal disease viruses].

The full-length of segment A of three infectious bursal disease viruses (IBDV), including an attenuated strain HZ2, an attenuated vaccine strain JD1 and a virulent field isolate ZJ2000, were cloned by long RT-PCR and sequenced respectively. All the three results revealed the identity of IB-DV with two overlapping open reading frames (ORF) flanked by 5'- and 3'-noncoding regions(NCR) in 3259 bp long. The strains shared high identity with each other at nucleotide or deduced amino acid level, and also had four unique sites H253, N279, T284, R330 which are common in other attenuated and some classic or highly virulent strains. The virulent strain ZJ2000 had several key amino acid mutations located in hypervariant region of VP2 and near the VP2-VP4 cleavage site of polypeptide, which is probably related to the virulence. Sequence comparison supported that VP2 is not the sole determinant of the virulence. The highly conservation in 5'- and 3'-NCR of different strains indicated the NCR may be not responsible for the virulence. But the same conservation appeared in VP5 revealed another complex relationship between VP5 and the virulence.