Purification and characterization of bovine rotavirus cores.

Using the chaotropic effect generated by a high concentration of CaCl2, we converted calf rotavirus particles into cores of 40 nm in diameter. These cores were purified by rate zonal centrifugation in sucrose gradients and by isopycnic gradients. They had a sedimentation coefficient of 280S +/- 20S and a density of 1.44 g/ml in CsCl. When analyzed by polyacrylamide gel electrophoresis, they contained three polypeptides (VP125, VP89, and VP78). The major internal polypeptide of the virion (VP39) was recovered in a purified and soluble form in the top fractions of the sucrose gradients. From this stepwise degradation, it appears that VP39 is the most external polypeptide of dense particles. In contrast to reovirus cores, calf rotavirus cores did not exhibit transcriptase activity. Purified VP39 also did not exhibit transcriptase activity when tested after being mixed with purified rotavirus genome RNA as a template. Transcriptase activity was partially recovered when ionic conditions were adjusted to permit the reassociation of VP39 with the cores.