Synthesis, stability, and cleavage of Newcastle disease virus glycoproteins in the absence of glycosylation

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Abstract
Polypeptides synthesized in Newcastle disease virus (NDV)-infected [Chinese hamster ovary] CHO cells in the absence of glycosylation were characterized. Incorporation of either [3H]mannose or [3H]glucosamine into NDV polypeptides was inhibited to greater than 99% by the antibiotic tunicamycin. Under these conditions, infected cells synthesized proteins which comigrated on polyacrylamide gels with the viral L protein, nucleocapsid protein, membrane protein and a polypeptide with a MW of 55,000 (P55). These cells did not synthesize polypeptides with the size of the hemagglutinin-neuraminidase (HN) protein or the fusion (F0) protein. They did synthesize new polypeptides with MW of 75,000 (P75), 67,000 (P67) and 52,000 (P52). Peptide analysis revealed that P75 was a host cell protein whose synthesis is enhanced by tunicamycin. P67 corresponded to the unglycosylated HN protein, and P52 corresponded to a cleaved, unglycosylated form of F0. These unglycosylated forms of the glycoproteins were relatively stable in infected cells. P55, previously thought to correspond to the cleaved form of F0, was a unique viral protein which is associated with intracellular nucleocapsid structures.