Cloning and expression of the VP2 gene of an infectious bursal disease virus.

A serotype I infectious bursal disease virus (IBDV) strain HZ96 was isolated in Hangzhou, China, in 1996 and attenuated by adaptation to chicken embryo fibroblast cells. The VP2 gene of strain HZ96 was amplified by reverse transcription-polymerase chain reaction, cloned, and sequenced. Compared with the VP2 sequences of other IBDV strains, HZ96 is most related to two attenuated strains, CU-1 and PBG98, and two attenuated Chinese strains, Harbin and CJ801bkf. HZ96 shares nucleotide sequence homology 98.9% with CU-1 and PBG98, 98.5% with Harbin, and 98.6% with CJ801bkf. Most of the sequence variations observed between HZ96 and other strains are located in the middle variable region from nucleotides 637 to 996. Similar to other attenuated IBDVs, HZ96 has unique substitutions at residues 279 (Asp to Asn) and 284 (Ala to Thr), suggesting that these two substitutions may be directly related to adaptation of the virus to cell culture and attenuation of its virulence. As part of our effort to develop a submit vaccine for IBDV, the VP2 gene of HZ96 was cloned into a heat-inducible expression vector and expressed in Escherichia coli system. A protein band with expected molecular weight of 52 kD was detected by direct protein staining and western blotting.