Characterisation of murine pneumonia virus proteins.

Twelve ³⁵S]methionine-labelled polypeptides ranging in molecular weight from 12,000 to 191,000, which were not present in mock-infected BS-C-1 cells, were detected in cells infected with murine pneumonia virus (PVM). All but two of these polypeptides were present in cell-released virus concentrated by polyethylene glycol precipitation and partially purified by equilibrium centrifugation. Two major glycopolypeptides, VPII (79,000 mw) and VPIII (68,000 mw) were present in partially purified virus but only VPII was prominent intracellularly. Nucleocapsids were isolated from lysates of infected cells by centrifugation in a gradient of 15–50% metrizamide and contained a major (VPIV) and a minor (VPVI) polypeptide with molecular weights of 42,300 and 35,700, respectively. Polypeptides with the electrophoretic mobilities of six of the PVM polypeptides (VPIV, VPV, VPVII, VPIX, VPX, and VPXI) were detected by in vitro translation of cytoplasmic RNA from PVM-infected cells in a cell-free system prepared from rabbit reticulocytes. PVM resembled RS virus, the other member of the pneumovirus genus, in its ability to multiply in enucleate cells. It is distinguished, however, by its four low molecular weight polypeptides (VPIX, VPX, VPXI, and VPXII), which appear to be primary gene products, and by the different electrophoretic mobility of the glycopolypeptides (VPII and VPIII).