[Molecular drift of rotavirus during attenuation]

The genome structure and polypeptide composition of a rotavirus virion isolated from piglets is described. Proteins p90 and p38 were localized in the external capsid of the virion, and the group-specific antigen of rotaviruses, protein p42, in the internal capsid. Minor polypeptides p116, p98, and p92 were associated with the virus core. A scheme of the structure of porcine rotavirus virion is proposed on the basis of the virion ultrastructure and localization of viral proteins in the capsid. Attention is drawn to the fact that the "wild" strain of swine rotavirus which is virulent for piglets differed in electrophoretic mobility of at least 3 segments of virus genome from the same strain which had undergone 70 passages in cell culture. The virus with altered RNA-segments showed no virulence. The change in the molecular weight of the RNA-segment 4 correlated with the change in polypeptide p90 coded for by it. In the authors' opinion, variability of the major product of protein p90 proteolysis caused the loss of rotavirus virulence for the naturally susceptible host.