Summary auto-generated
This study examined the distribution and sequence variation of NV (non-virion) genes among fish rhabdoviruses. The NV gene, which encodes a non-virion protein expressed in infected cells but absent from mature virions, was previously known only in infectious haematopoietic necrosis virus (IHNV). Researchers analyzed the genome region between the glycoprotein (G) and polymerase (L) genes in three additional fish rhabdoviruses. They found that hirame rhabdovirus (HIRRV) contains an NV gene closely related to IHNV's (63% nucleotide identity), while viral haemorrhagic septicaemia virus (VHSV) has a significantly diverged NV gene. Critically, spring viraemia of carp virus (SVCV), the only vesiculovirus-like fish rhabdovirus examined, lacks an NV gene entirely at the G–L junction, containing only four nucleotides (CTAT). These findings suggest that NV genes are characteristic of the unassigned fish rhabdovirus subgroup (formerly classified as lyssaviruses) and support establishing this group as an independent genus. Since SVCV replicates in fish cells without an NV gene, the NV protein is not essential for viral replication in fish cells per se.
Key findings
- All three unassigned fish rhabdoviruses (IHNV, HIRRV, and VHSV) contain NV genes at their G–L junctions, whereas the vesiculo-like fish rhabdovirus SVCV lacks an NV gene entirely.
- HIRRV's NV gene is closely related to IHNV's NV gene (54.1% amino acid identity, 72.1% similarity), while VHSV's NV gene is significantly diverged (23.3–47.6% identity with IHNV/HIRRV).
- The presence of an NV gene is proposed as a genetic hallmark distinguishing unassigned fish rhabdoviruses from vesiculovirus-like fish rhabdoviruses, supporting the classification of unassigned viruses as a separate genus.
- The NV gene is not essential for viral replication in fish cells, as demonstrated by SVCV's successful replication without it.
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Abstract
The fish rhabdovirus infectious haematopoietic necrosis virus (IHNV) contains a non-virion (NV) gene between the glycoprotein (G) and polymerase (L) genes on its RNA genome. The present study investigated three other fish rhabdovirus genomes and found that the NV gene of hirame rhabdovirus is closely related to the NV of IHNV, whereas the viral haemorrhagic septicemia NV gene showed evidence of significant divergence. Most importantly, spring viraemia of carp virus, the only vesiculovirus-like fish rhabdovirus examined, did not have an NV gene at its genomic RNA G-L junction. These results suggest that the presence of an NV gene is characteristic of the unassigned fish rhabdovirus subgroup previously classified as lyssaviruses, and that the NV gene is not essential for replication in fish cells per se, since it is absent in a vesiculovirus-like fish rhabdovirus.