The polypeptides of mumps virus and their synthesis in infected chick embryo cells

Abstract

The polypeptides of mumps virus grown in chick embryo (CE) cells were analyzed by polyacrylamide gel electrophoresis and partial proteolytic mapping. The virus contains five unique polypeptides, gp80(HN), p73(NP), gp61(F 1), p45, and p39, and an additional few minor species, p71, p47, and p42. Except for p45 and p42 they were remarkably phosphorylated. The polypeptide p71 was related to p73 and these two proteins comigrated on the gels in the presence of urea. There was also a close relationship between p47 and p45 and the former was a phosphorylated form of the latter. The polypeptide p42 was suggested to be actin derived from the host cell. Under nonreducing conditions of electrophoresis, the glycoprotein F(gp73) was identified, which consisted of two disulfide bonded glycopeptides, F 1 and F 2(gp10). The development of viral proteins in infected CE cells was analyzed by immunoprecipitation followed by polyacrylamide gel electrophoresis. It was demonstrated that p45 was synthesized very early in infection and rapidly reached the maximal rate of synthesis. In contrast, the appearance of the other polypeptides was delayed and their synthesis rates were found to increase with time until a very late stage. Thus the patterns of early and late protein synthesis were largely different from each other, suggesting a distinct temporal regulation in the mumps virus protein synthesis. Pulse-chase experiments demonstrated that the glycoprotein F would be formed by proteolytic cleavage of a precursor glycoprotein F 0 with an apparent molecular weight of 73,000. No other proteolytic processing has been found.