Molecular characterization of Sp serotype strains of infectious pancreatic necrosis virus exhibiting differences in virulence.
Infectious pancreatic necrosis virus (IPNV), a prototype virus of the family Birnaviridae, exhibits a high degree of antigenic variability, pathogenicity and virulence in salmonid species. The Genomic Segment A encodes all the structural (VP2 and VP3) and nonstructural (NS) proteins, whereas Segment B encodes the viral RNA-dependent RNA polymerase (VP1). We tested 3 different IPNV isolates (Sp103, Sp116 and Sp122) isolated during field outbreaks in Norway for their ability to cause mortality in fry and post-smolt of Atlantic salmon Salmo salar L. The cumulative mortality following experimental challenge in fry was 29% for Sp122 followed by 19% for Sp116 and 15% for Sp103. In post-smolt, the corresponding mortality rates were 79, 46 and 16%, respectively. Comparisons of the deduced amino acid sequences of Segments A and B of all 3 Sp strains revealed substitutions of residues in 13 positions, of which 6 are in VP2, 2 in VP3, and 5 in VP1. Our results suggest that these residues, especially those in the outer capsid VP2, may be involved in the virulence of IPNV. Genome Segment A of the Sp serotype is 3097 nucleotides long and contains a major open reading frame (ORF) encoding a polyprotein of 972 amino acids, which initiates at the second in-frame start codon at Position 119. This was ascertained by making mutants of Segment A clone using site-directed mutagenesis, followed by in vitro transcription-coupled translation reaction and immunoprecipitation analyses. In addition, Segment A also encodes a 15 kDa arginine-rich non-structural protein from a small ORF, preceding and partially overlapping the polyprotein ORF, which is truncated to 12 kDa in the virulent Sp122 strain. Moreover, Segment A could encode a novel, putative 25 kDa protein from another ORF between VP2 and VP4 coding regions, which is only detected in the Sp serotype. Segment B is 2777 nucleotides long and encodes in a single large ORF (a polypeptide of 844 amino acid residues), VP1.
Shivappa
R B
RB
Center for Biosystems Research, University of Maryland Biotechnology Institute and VA-MD Regional College of Veterinary Medicine, University of Maryland, College Park, Maryland 20742, USA.
Song
H
H
Yao
K
K
Aas-Eng
A
A
Evensen
O
O
Vakharia
V N
VN
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018175:Birnaviridae Infections / Q000401:mortality / Q000662:veterinary*; D003001:Cloning, Molecular; D016000:Cluster Analysis; D005393:Fish Diseases / Q000401:mortality / Q000821:virology*; D047468:Immunoprecipitation / Q000662:veterinary; D018061:Infectious pancreatic necrosis virus / Q000235:genetics* / Q000472:pathogenicity*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009664:Norway; D009841:Oligonucleotides; D020317:Salmo salar; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA / Q000662:veterinary; D013045:Species Specificity; D014764:Viral Proteins / Q000235:genetics*; D014774:Virulence / Q000235:genetics
D009841:Oligonucleotides; D014764:Viral Proteins