Genome cloning and analysis of the large RNA segment (segment A) of a naturally avirulent serotype 2 infectious bursal disease virus

The genome of infectious bursal disease virus (IBDV) of serotype 2 (strain OH) has been cloned, and 3171 nucleotides of genome segment A cDNA sequence have been determined for the first time. Sequence homology of OH-IBDV with the most distant serotype 1 IBDV at the nucleotide level is 83.1%, and the amino acid sequence homology of the polyprotein is 89.6%. Alignment of the polyprotein amino acid sequences showed the hypervariable region in VP2 to be 151–152 amino acid residues long in IBDV. A second variable region, 37 amino acid residues long, was identified in the N-terminal third of the IBDV VP2 molecule. IBDV strains, like the IPNV strains, also contain inverted repeats that may form stem-and-loop structures in the 5′ noncoding sequences. These inverted repeats are variable between the two IBDV serotypes, particularly at the AT basepairs.