title: Identification and analysis of truncated and elongated species of the flavivirus NS1 protein.
abstract: The flavivirus non-structural glycoprotein NS1 is often detected in Western blots as a heterogeneous cluster of bands due to glycosylation variations, precursor-product relationships and/or alternative cleavage sites in the viral polyprotein. In this study, we determined the basis of structural heterogeneity of the NS1 protein of Murray Valley encephalitis virus (MVE) by glycosylation analysis, pulse-chase experiments and terminal amino acid sequencing. Inhibition of N-linked glycosylation by tunicamycin revealed that NS1 synthesised in MVE-infected C6/36 cells was derived from two polypeptide backbones of 39 kDa (NS1(o)) and 47 kDa (NS1'). Pulse-chase experiments established that no precursor-product relationship existed between NS1(o) and NS1' and that both were stable end products. Terminal sequencing revealed that the N- and C-termini of NS1(o) were located at amino acid positions 714 and 1145 in the polyprotein respectively, consistent with the predicted sites based upon sequence homology with other flaviviruses. Expression of the NS1 gene alone or in conjunction with NS2A by recombinant baculoviruses demonstrated that the production of NS1' was dependent on the presence of NS2A, indicating that the C-terminus of the larger protein was generated within NS2A. A smaller form (31 kDa) of NS1 (deltaNS1) was also identified in MVE-infected Vero cultures, and amino acid sequencing revealed a 120-residue truncation at the N-terminus of this protein. This corresponds closely with the in-frame 121-codon deletion at the 5' end of the NS1 gene of defective MVE viral RNA (described by Lancaster et al. in 1998), suggesting that deltaNS1 may be a translation product of defective viral RNA.
authors.affiliation: Department of Microbiology, The University of Western Australia, QE-II Medical Centre, Nedlands, Australia. bblitvic@sunflower.bio.indiana.edu
authors.forename: B J
authors.initials: BJ
authors.lastname: Blitvich
authors.forename: D
authors.initials: D
authors.lastname: Scanlon
authors.forename: B J
authors.initials: BJ
authors.lastname: Shiell
authors.forename: J S
authors.initials: JS
authors.lastname: Mackenzie
authors.forename: R A
authors.initials: RA
authors.lastname: Hall
mesh_terms: D000330:Aedes / Q000166:cytology; D000595:Amino Acid Sequence; D000818:Animals; D016367:Baculoviridae; D002241:Carbohydrates / Q000032:analysis; D002460:Cell Line; D002522:Chlorocebus aethiops; D018068:Encephalitis Virus, Murray Valley / Q000378:metabolism*; D015870:Gene Expression; D005822:Genetic Vectors; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D018411:Spodoptera / Q000166:cytology; D014709:Vero Cells; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D002241:Carbohydrates; C100315:NS1 protein, Flavivirus; D010455:Peptides; D011993:Recombinant Fusion Proteins; D017361:Viral Nonstructural Proteins