The P gene of Newcastle disease virus does not encode an accessory X protein

Abstract

Many paramyxoviruses encode non-essential accessory proteins that are involved in the regulation of virus replication and inhibition of cellular antiviral responses. It has been suggested that the P gene mRNA of Newcastle disease virus (NDV) encodes an accessory protein -the so-called X protein -by translation initiation at a conserved in-frame AUG codon at position 120. Using a monoclonal antibody that specifically detected the P and X proteins, it was shown that an accessory X protein was not expressed in NDV-infected cells. Recombinant NDV strains in which the AUG was changed into a GCC (Ala) or GUC (Val) codon were viable but showed a reduction in virulence, probably because the amino acid change affected the function of the P and/or V protein.The family Paramyxoviridae includes important pathogens that can cause severe disease in humans as well as animals. Well-known examples of human pathogens are measles virus, mumps virus, Hendra virus and Nipah virus. Animal pathogens include rinderpest virus, bovine respiratory syncytial virus and Newcastle disease virus (NDV). The subfamily Paramyxovirinae consists of five genera, Respirovirus, Morbillivirus, Rubulavirus, Henipavirus and Avulavirus (Mayo, 2002a, b). Paramyxoviruses have a non-segmented negative-sense single-stranded RNA genome that encodes six to ten genes (Lamb & Kolakofsky, 2001). Characteristic of most, if not all, paramyxoviruses is the ability to generate multiple proteins from the P gene. These so-called accessory proteins are generated by an RNA-editing event and in some instances by the use of alternative open reading frames (ORFs) present within the P gene. For respiroviruses, morbilliviruses and avulaviruses, the P protein is encoded by an unedited transcript of the P gene, whereas the V and W proteins are the result of an mRNA-editing event in which one (V) or two (W) G residues are inserted at a specific position within the P gene mRNA. For rubulaviruses, the unedited mRNA generates the V protein while the P and W proteins are the result of mRNAediting. Additional proteins derived from the P gene mRNA may be generated by translation initiation at different start points in the +1 reading frame (C proteins) or in the same reading frame (X protein) (Curran et al., 1998). Morbilliviruses express at least one C protein, whereas some respiroviruses express two or more. Apart from the P protein, the Sendai virus P gene seems to encode a total of at least seven accessory proteins, i.e. V and W by RNA-editing, C, C9, Y1 and Y2 from the +1 reading frame, and X from an in-frame reading frame (Curran et al., 1998).Expression of an accessory C protein, or X protein, has not yet been reported for rubulaviruses or avulaviruses. However, McGinnes et al. (1988) reported the existence of 38 and 29 kDa non-structural proteins derived from the P gene ORF of NDV (genus Avulavirus) and suggested that these proteins could have been generated by in-frame translation initiation at amino acid positions 82 and 120, respectively. Analysis of the P gene sequences of...

Regulation of translation via mRNA structure in prokaryotes and eukaryotes

“…15 mRNA cleavage might explain why upORFs which strongly inhibit translation in vivo are sometimes less inhibitory in vitro (Ghilardi et al, 1998;Meijer et al, 2000;Pecqueur et al, 2001;Tanaka et al, 2001) and why translation sometimes initiates in vitro at fardownstream AUG codons which are not used in vivo (Byrd et al, 2002, Fig. 3C;Hassin et al, 1986;Meulewaeter et al, 1992;Peeters et al, 2004). In vitro translation reactions that generate an array of low molecular weight polypeptides are a sure sign of mRNA degradation (e.g.…”

The Large Polymerase Protein Is Associated with the Virulence of Newcastle Disease Virus

“…It encodes at least six proteins: the nucleocapsid protein (N), the phosphoprotein (P), the matrix protein (M), the fusion protein (F), the hemagglutinin-neuraminidase protein (HN), and the large polymerase protein (L) (4,29). Two additional proteins, V and W, are produced by RNA editing during P gene transcription (21,27). The M, F, and HN proteins are associated with the virus envelope, and the latter two are the protective antigens of NDV.…”

Identification of a truncated nucleoprotein in avian metapneumovirus-infected cells encoded by a second AUG, in-frame to the full-length gene

“…Consequently, during translation there is a frame shift resulting in production of the V or W protein, dependent on the number of G nucleotides inserted [12]. It was previously suggested that NDV [26] potentially utilized an alternative in-frame AUG start site for expression of an accessory protein similar to the Sendai virus X protein [21] that was recently demonstrated to not be utilized during infection of cells in culture [27]. …”