Composition and topography of structural polypeptides of bovine rotavirus

The composition and topography of the structural polypeptides of bovine rotavirus was studied by polyacrylamide gel electrophoresis of radioactively labelled virus grown in LLC-MK2 cells and by lactoperoxidase-catalysed iodination of single- and double- capsid particles. Bovine rotavirus was found to possess at least six structural polypeptides, three of them associated with the inner capsid (p102K, p91K and p45K) and the others with the outer capsid (p84K, p37K and p34K). The most abundant polypeptide of the inner capsid was p45K, which accounted for approx, 80% of the protein mass, followed by p91K (approx, 20% of the protein mass) and p102K (approx. 1% of the protein mass). Polypeptide 45K is not readily available for iodination, indicating that it is partially covered by p91K, which is the most exposed polypeptide of the inner capsid. The number of polypeptide molecules per single capsid particle (calculated on the basis of an RNA content of 16%) was estimated to be approx. 6 molecules of p102K, 140 of p91K and 989 of p45K. The stoichiometry and degree of exposure of outer capsid polypeptides was more difficult to establish, even when it appears that p84K and p34K are the most exposed components.