The putative polymerase sequence of infectious salmon anemia virus suggests a new genus within the Orthomyxoviridae

The infectious salmon anemia virus (ISAV) is an orthomyxovirus-like virus i nfecting teleosts. The disease caused by this virus has had major economic consequences for the Atlantic salmon farming industry in Norway, Canada, an d Scotland. In this work, we report the cloning and sequencing of an ISAV-s pecific cDNA comprising 2,245 bp with an open reading frame coding for a pr edicted protein with a calculated molecular weight of 80.5 kDa. The putativ e protein sequence shows the core polymerase motifs characteristic of all v iral RNA-dependent RNA polymerases. Comparison of the conserved motifs with the corresponding regions of other segmented negative-stranded RNA viruses shows a closer relationship with members of the Orthomyxoviridae than with viruses in other families. The putative ISAV polymerase protein (PB1) has a length of 708 amino acids, a charge of +22 at neutral pH, and a pI of 9.9 , which are consistent with the properties of the PB1 proteins of other mem bers of the family. Calculations of the distances between the different PB1 proteins indicate that the ISAV is distantly related to the other members of the family but more closely related to the influenza viruses than to the Thogoto viruses. Based on these and previously published results, we propo se that the ISAV comprises a new, fifth genus in the Orthomyxoviridae.