Molecular cloning, sequence analysis, in vitro expression, and immunoprecipitation of the major inner capsid protein of the IDIR strain of group B rotavirus (GBR).

The sixth genomic segment of the infectious diarrhea of infant rats (IDIR) strain of group B rotavirus (GBR) was cloned from double-stranded RNA purified from infected rat feces. Sequence comparison with group A rotaviruses (GAR) and the human ADRV strain of GBR indicated that IDIR gene 6 encoded the major inner capsid protein. The nucleic acid sequences of the two GBR genes were 72.9% conserved, and 83.4% of the amino acids were identical. Sequence substitutions between IDIR and ADRV were more numerous than reported for heterologous GAR strains, indicating that the two GBR strains may have diverged from one another over a longer period of time. Despite the sequence heterogeneity exhibited by the major inner capsid proteins of ADRV and IDIR, hydrophilicity plots of the two gene products were nearly indistinguishable. The GBR hydrophilicity plots displayed little similarity with those of rotavirus groups A or C, indicating substantial differences in the structures of those major inner capsid proteins. In vitro transcription and translation of IDIR gene 6 yielded a polypeptide product consistent in size with that predicted from the deduced amino acid sequence and the virion major inner capsid protein. The IDIR 6 polypeptide was immunoprecipitated by antisera directed against IDIR as well as antisera directed against ADRV and a heterologous bovine strain of GBR. No immunoprecipitation was observed with control sera or antisera directed against GAR. These results confirmed that group-specific epitopes were displayed by the major inner capsid protein encoded by IDIR gene 6. Reactivity with heterologous GBR antisera also indicated that the IDIR gene 6 product may prove useful as a standard reagent in immunoassays for the detection of GBR.