ANALYSIS OF THE SEROTYPE-SPECIFIC EPITOPES OF AVIAN INFECTIOUS-BRONCHITIS VIRUS-STRAINS ARK99 AND MASS41

The Ark and Mass serotype-specific epitopes of infectious bronchitis v irus were studied by immunofluorescence and immunoprecipitation of mut ant acid recombinant spike glycoproteins (S protein) expressed in mous e L cells. Serotype-specific monoclonal antibodies could bind to the r ecombinant proteins of Ark99 and Mass41 expressed from the chimeras in which the N-terminal thirds of the S1 sequences were reciprocally exc hanged. Therefore, it appears that the respective serotype-specific ep itopes of both strains were localized within the C-terminal two-thirds of the S1 proteins. Deletion and insertion of a five-amino-acid fragm ent on the S1 proteins of Ark99 and Mass41 altered the serotype-specif ic epitopes. This result implies that the five-aminoacid insertion on the S1 protein of the Ark serotype was involved in determining the con formation of the protein, probably acting as a spacer. In addition, it appears that an interaction between sequences of the N-terminal third and the remaining portion of the S1 protein determines the tertiary s tructure of the protein as well as the conformation of the serotype-sp ecific epitope.