Identification and expression of the outer capsid protein (VP4) of the IDIR strain of group B rotavirus.

The polypeptide encoded by gene 3 of the IDIR strain of group B rotavirus (GBR) was synthesized by means of a baculovirus expression system. Immunoblot analysis identified the IDIR virus gene 3 product as analogous to the outer capsid protein, VP4, encoded by gene 4 of group A rotaviruses (GAR). This coding assignment had previously been difficult to establish by sequence comparisons, since IDIR virus gene 3 shared < 20% identical amino acid sequences with any GAR protein. Trypsin digestion of the gene 3 protein resulted in the appearance of a product indistinguishable in size from the VP5* outer capsid protein of IDIR agent virions. The recombinant IDIR virus VP4 maintained at least some antigenic epitopes of the native virion protein, as evidenced by reactivity with convalescent antibody obtained following infection of infant rat pups with the IDIR agent. Reactivity was also demonstrated with antisera directed against bovine and porcine isolates of GBR as well as with ADRV, a human strain of GBR.