of family
Birnaviridae|rightThe genome is composed of linear, bi-segmented, double-stranded RNA. It is around 5.9–6.9 kbp in length and codes for five to six proteins. Birnaviruses encode the following proteins:
RNA-directed RNA polymerase (VP1), which lacks the
highly conserved Gly-Asp-Asp (GDD) sequence, a component of the proposed
catalytic site of this enzyme family that exists in the
conserved motif VI of the palm domain of other RNA-directed RNA polymerases. The large RNA segment, segment A, of birnaviruses
codes for a
polyprotein (N-VP2-VP4-VP3-C) that is processed into the major structural
proteins of the virion: VP2, VP3 (a minor structural component of the virus), and into the putative
protease VP4.
Infectious pancreatic necrosis virus (IPNV), a birnavirus, is an important
pathogen in
fish farms. Analyses of
viral proteins showed that VP2 is the major
structural and immunogenic
polypeptide of the virus. All
neutralizing monoclonal antibodies are specific to VP2 and
bind to continuous or discontinuous
epitopes. The variable domain of VP2 and the 20 adjacent
amino acids of the
conserved C-terminal are probably the most important in inducing an
immune response for the protection of
animals. Non
structural protein VP5 is found in RNA segment A. VP5 is not essential for replication. ==Viral Replication==