Measles viral envelope proteins were immune precipitated from membranes of infected cells and from purified virus and analyzed by
polyacrylamide gel electrophoresis. Under reducing conditions, specific precipitates contained two major
polypeptide bands, designated virus
glycopeptides 1 and 2 (VGP-1 and VGP-2). Both
polypeptides appeared to be glycosylated, as indicated by their incorporation of [(14)C]
glucosamine in infected cells. VGP-2 appeared as a single band in specific precipitates of infected cells and as a double band in precipitates of purified virus.
Trypsin treatment of infected cells showed that reduced VGP-2 may be composed of two unrelated
polypeptides. One may be F(1), which is unglycosylated, and the other may correspond to the proteolytic cleavage product of VGP-1, which is glycosylated. The relation of VGP-1 and VGP-2 to smaller
surface antigens (X and Y) obtained by tryptic treatment of infected cells remains to be elucidated. In cells taken at various times postinfection and analyzed for
viral membrane proteins, VGP-1 was detected at all times, indicating that the input virus VGP-1 was inserted into the cell and could not be differentiated from newly synthesized VGP-1. VGP-2 was not detectable before 24 h postinfection. In precipitates of cells 4 h postinfection and of infected cells incubated at pH 5.8, an additional
polypeptide band migrated immediately ahead of VGP-1. We conclude that VGP-2 (molecular weight, 42,000) possibly consists of two components, one of which is the tryptic cleavage product of VGP-1 and the other of which is the unglycosylated
polypeptide, F(1).