B2 protein from betanodavirus is expressed in recently infected but not in chronically infected fish.

Betanodavirus infects both larvae and juvenile fish and can cause the disease viral encephalopathy and retinopathy (VER). During an acute outbreak of VER, infected individuals display several clinical signs of infection, i.e. abnormal swimming pattern and loss of appetite. Betanodaviruses can also cause chronic or persistent infection where the infected individuals show no clinical signs of infection. During infection the viral sub-genomic RNA3 and the RNA3-encoded B2 protein are expressed. Antibodies against the B2 protein from Atlantic halibut nodavirus were raised and used together with antibodies against the capsid protein to detect the presence of these 2 viral proteins in infected cells in culture and at different stages of infection in Atlantic halibut Hippoglossus hippoglossus and Atlantic cod Gadus morhua. The B2 protein was detected in recently infected, but not in chronically infected fish. Results suggest that the detection of B2 may be used to discriminate a recent and presumably active infection from a chronic and presumably persistent infection.

RNA-dependent RNA polymerase from Atlantic halibut nodavirus contains two signals for localization to the mitochondria.

Nodaviruses encode an RNA-dependent RNA polymerase called Protein A that is responsible for replication of the viral RNA segments. The intracellular localization of Protein A from a betanodavirus isolated from Atlantic halibut (AHNV) was studied in infected fish cells and in transfected mammalian cells expressing Myc-tagged wild type Protein A and mutants. In infected cells Protein A localized to cytoplasmic structures resembling mitochondria and in transfected mammalian cells the AHNV Protein A was found to co-localize with mitochondrial proteins. Two independent mitochondrial targeting signals, one N-terminal comprising residues 1-40 and one internal consisting of residues 225-246 were sufficient to target both Protein A deletion mutants and enhanced green fluorescent protein (EGFP) to the mitochondria. The N-terminal signal corresponds to the mitochondrial targeting sequence of the Flock House Virus (FHV) Protein A while the internal signal is similar to the single targeting signal previously found in Greasy Grouper Nervous Necrosis Virus (GGNNV) Protein A.