Proteins induced in Newcastle disease virus (NDV)-infected chick embryo fibroblasts (CEF) and proteins incorporated into virions grown were analysed by modified versions of a two-dimensional polyacrylamide gel electrophoresis system. The following previously described NDV-induced proteins were detected and resolved from host proteins: L (mol. wt. approx. 200K), HN (75K), F (66K), F (56K), NP (55K) and M (39K). Two additional polypeptides, NAP (nucleocapsid-associated protein, mol. wt. 56K) and a 36 K mol. wt. protein were induced in NDV-infected cells. NAP but not 36K was found in purified virions. Radioactive labelling studies with H-glucosamine and P-orthophosphate demonstrated that neither NAP nor 36K is glycosylated, but that both are phosphorylated.

Variation in the isoelectric point and apparent mol. wt. of NAP among different strains was seen and exactly reproduced in both CEF and baby hamster kidney (BHK) cells. The synthesis of NDV-induced proteins including NAP and 36K was unaffected by actinomycin D, whereas the synthesis of host cell proteins was drastically reduced. These data are evidence that NAP and 36K are virus coded. Peptide analysis indicated that NAP, NP and F are unrelated polypeptides. The demonstration that NAP is virus coded, together with its phosphorylation and association with the nucleocapsid, suggest that NAP may be the NDV analogue of the P protein of Sendai virus.


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