Separation and infectivity of two particle types of human rotavirus.

Two morphological types of human rotavirus particles were separated in caesium chloride density gradients. The particles of higher density ('incomplete' particles without an outer capsid layer) banded at a density of 1-38 g/ml, while the less dense ('complete' particles with an outer as well as an inner capsid layer) banded at a density of 1-36 g/ml. Some particles were found with an incomplete outer layer of capsomeres. The particle/infectivity ratio for tissue cultures of the fraction containing complete particles was more than 3 log10 higher than that of the fraction containing incomplete particles. But, as there was a small number of complete particles in the fraction containing mostly incomplete particles, it was impossible to determine whether the incomplete particles had a low infectivity or whether they had none at all.