Sequence of precursor polyprotein gene (segment A) of infectious bursal disease viruses isolated in Korea

The coding regions of segment A of two recent Korean very virulent (vv) infectious bursal disease virus (IBDV) isolates (KK1 and KSH) and one atypical IBDV isolate (K310) were amplified by reverse transcriptase-polymerase chain reaction, sequenced, and compared with published sequences for IBDV. The overall amino acid sequence similarity of the KK1 and KSH strains compared with foreign vvIBDV strains was between 97.43% and 98.02%. The KK1 and KSH strains, like vvIBDV strains, share unique amino acid residues at positions 222(A), 256(I), 294(I), and 299(S). The sequence of K310 strain was markedly different from other IBDV strains. The K310 strain had 12, 2, and 1 unique amino acid substitutions in the VP2 hypervariable region, VP4, and VP3 gene, respectively, and 3 of 12 substitutions in a VP2 hypervariable region were found in two hydrophilic regions known to be involved in antigenic determination. Also, the K310 strain had 222(S) and 254(S), which were found in variant IBDV strains. The SWSASGS heptapeptide is conserved in all Korean IBDV isolates. By phylogenetic analysis, KK1 and KSH were categorized in one group with foreign vvIBDV isolates, but K310 isolate was categorized in a separate group that was differentiated from the other IBDV strains compared. The K310 strain seemed to be evolved from a separate lineage of IBDV strain.