Deletion mapping and expression in Escherichia coli of the large genomic segment of a birnavirus.

The large genomic segment of infectious bursal disease virus encodes a polyprotein in which the viral polypeptides are present in the following order: N-VP2-VP4-VP3-C. Expression in Escherichia coli of the large segment results in the processing of the polyprotein. The expression product reacts with a virus neutralizing and protective monoclonal antibody that recognizes a conformational epitope on the surface of the virus. Different regions of the large genomic segment were deleted at defined restriction sites and the truncated fragments were ligated to various expression vectors for high-level expression in E. coli. The expressed proteins were probed with three different monoclonal antibodies that recognize epitopes encoded by different regions of the large genomic segment. These deletion mapping studies suggest that VP4 is involved in the processing of the precursor polyprotein, and the conformational epitope recognized by the virus neutralizing monoclonal antibody is present within VP2.