Submitted to: Virology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2005
Publication Date: 4/12/2005
Citation: Seal, B.S., Alvarez, R. 2005. Identification of a truncated nucleoprotein in avian metapneumovirus-infected cells encoded by a second aug, in-frame to the full-length gene. Journal of Virology. 2(1):31. Interpretive Summary: Avian metapneumoviruses (aMPV) cause an upper respiratory tract disease designated turkey rhinotracheitis (TRT). The disease TRT in commercial turkeys does not usually cause death, but symptoms can be more severe when accompanied by secondary bacterial infections. Prior to 1996 the disease was not found in the United States or other regions of North America. However, a new viral subtype C different from European subtype A and B viruses is now present among commercial United States turkey flocks. Reagents utilized to detect these viruses have been developed that recognize proteins of aMPV isolates, specifically a series of antibodies to the nucleoprotein (N) of the virus. The N protein is important for the virus to replicate and varies little in its amino acid composition from one aMPV isolate to another. Consequently, these antibodies have been utilized for diagnostic reagents to detect the virus in clinical samples. During development of these reagents two separate proteins were detected utilizing antibodies to detect the tail-end or C-terminus of the N protein for aMPV isolates. This is a unique finding in that this is the first report of a second or alternative accessory gene product in the N gene of these virus types.
Technical Abstract: The presence of two avian metapneumovirus (aMPV) nucleoprotein (N) gene encoded polypeptides was identified in aMPV/C/US/Co and aMPV/A/UK/3b infected Vero cells. Nucleoprotein 1 (N1) encoded from the first open reading frame (ORF) was predicted to be 394 amino acids in length for aMPV/C/US/Co and 391 amino acids in length for aMPV/A/UK/3b with approximate molecular weights of 43.3 kilodaltons and 42.7 kilodaltons, respectively. Nucleoprotein 2 (N2) was hypothesized to be encoded by a second downstream ORF in-frame with ORF1 and encoded a protein predicted to contain 328 amino acids for aMPV/C/US/Co or 259 amino acids for aMPV/A/UK/3b with approximate molecular weights of 36 kilodaltons and 28.3 kilodaltons, respectively. Peptide antibodies to the N-terminal and C-terminal portions of the aMPV N protein confirmed presence of these products in both aMPV/C/US/Co- and aMPV/A/UK/3b-infected Vero cells. N1 and N2 for aMPV/C/US/Co ORFs were molecularly cloned and expressed in Vero cells utilizing eukaryotic expression vectors to confirm identity of the aMPV encoded proteins. Genomic sequence analyses of related members of the Pneumovirinae including human respiratory syncytial virus and bovine respiratory syncytial virus demonstrated the presence of this second potential ORF. This is the first reported identification of potential, in-frame N2 ORF gene products among members of the Paramyxoviridae.