The 36K polypeptide synthesized in Newcastle disease virus-infected cells possesses properties predicted for the hypothesized 'V' protein

Newcastle disease virus (NDV) virions possess two proteins which react strongly with monoclonal anti-body 688 following separation by high resolution two-dimensional (isoelectric focusing/SDS) PAGE and detection by Western blotting. One is the phosphory-lated nucleocapsid-associated 53K [P (NAP)] protein, the other comigrates with the 36K protein detected by radiolabelling NDV-infected chick embryo fibroblasts. [35S]Cysteine/[aH]leucine dual-labelling experiments show that the 36K protein is very rich in cysteine compared to the P (NAP) protein. In the Beaudette C strain it comigrates on one-dimensional SDS-poly-acrylamide gels with the matrix protein (M); however, it is resolved from the slower migrating M protein from the Ulster strain of NDV. The size, strain-specific isoelectric point, high cysteine content and antigenic relatedness to the P (NAP) protein suggest that the 36K protein is the 'V ' protein of NDV, the counterpart of which is found in other Paramyxoviridae. Newcastle disease virus (NDV) is a member of the genus paramyxovirus within the family Paramyxoviridae. Vir-ions contain six virus genome-encoded proteins: nucleo-capsid (NP) protein, the phosphorylated nucleocapsid-associated (P or NAP) protein, matrix (M) protein, fusion (F) protein, haemagglutinin-neuraminidase (HN) and the large polymerase (L) protein (Choppin & Compans, 1975; Samson, 1988). In addition several virus-encoded non-structural proteins have been detect-ed in NDV-infected cells, in particular the 36K protein (Chambers & Samson, 1980, 1982; Collins et al., 1982), the detailed genetic origin of which remains in doubt. The P genes of many members of the Paramyxoviridae have now been analysed and shown to be capable of encoding several proteins. Some viruses produce a C protein, which is encoded by an mRNA molecule containing two overlapping reading frames, e.g. Senda