Structure and replication of echovirus type 12. 1. Analysis of the polypeptides and RNA of echovirus 12 particles.

The propagation of echovirus 12 in green monkey kidney (GMK) cells, a continuous cell line, is described. Virions and empty capsids are purified to homogeneity by CsCl density and by velocity centrifugation. The protein composition of the particles as compared to poliovirus 2 particles is analyzed by dodecyl sulfate/polyacrylamide gel electrophoresis. Infectious virions were found to be composed of four different polypeptide chains of molecular weights 33,000, 31,000, 24,000 and 7,000. Some additional polypeptide bands at low concentrations are also visible. The empty capsids lack the 31,000-Mr and 7,000-Mr components and contain instead a polypeptide of the molecular weight 46,000. The molecular weights of the structural polypeptides are the same regardless of whether the virus has been synthesized in primary African green monkey kidney cells or in the continuous GMK cell line. The sedimentation behavior of echovirus 12 RNA is shown to be similar to that of poliovirus 2 RNA.