This superfamily entry includes the C-terminal extension domain of VP1 birnavirus RNA dependent RNA polymerase, characterised in IPNV (infectious pancreatic necrosis virus). Birnaviruses are dsRNA viruses and they are part of RNA-directed RNA polymerase family.

RNA-directed RNA polymerases (RdRp) (EC:2.7.7.48) are essential proteins encoded in the genomes of all RNA containing viruses with no DNA stage PMID:2759231,PMID:8709232.

The protein represented by this entry is VP1. All of the birnavirus VP1 proteins contain conserved RdRp motifs that reside in the catalytic "palm" domain of all classes of polymerases. However, the birnavirus RdRps lack 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 RdRps PMID:12069523.

In IPNV VP1, the N- and C-terminal extensions wrap around the core fingers, palm and thumb domains. The general conformation of the C-terminal extension is similar to IBDV (infectious bursal disease virus), passing from the inner-base of the thumb to the back of the fingers via the outer edge of the palm. However, many of the surface-exposed loops adopt different conformations and the helix-turn-helix between residues 736-779 is rotated relative to the equivalent region of IBDV VP1 PMID:21731487.

DOI:10.1371/journal.ppat.1002085,PFAM:PF04197,INTERPRO:IPR007100