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Updated: Aug 23, 2026

An Ex Vivo Chicken Primary Bursal-cell Culture Model to Study Infectious Bursal Disease Virus Pathogenesis
Published on: October 4, 2018
VP1 of infectious bursal disease virus is an RNA-dependent RNA polymerase
Ursula I von Einem1, Alexander E Gorbalenya2, Horst Schirrmeier3
1Institute of Molecular Biology, Federal Research Centre for Viral Diseases of Animals, Boddenblick 5a, 17493 Greifswald-Insel Riems, Germany.
Abstract:
Segment B of the bisegmented, double-stranded RNA genome of infectious bursal disease virus (IBDV) encodes the viral protein VP1. This has been presumed to represent the RNA-dependent RNA polymerase (RdRp) as it contains motifs that are typical for the RdRp of plus-strand RNA viruses. Here it is demonstrated that baculovirus-expressed wild-type but not motif A mutated VP1 acts as an RdRp on IBDV-specific RNA templates. Thus, on a plus-strand IBDV segment A cRNA template, minus-strand synthesis occurred in such a way that a covalently linked double-stranded RNA product was generated (by a 'copy-back' mechanism). Importantly, enzyme activity was observed only with templates that comprised the 3' non-coding region of plus-strand RNAs transcribed from IBDV segments A and B, indicating template specificity. RdRp activity was shown to have a temperature optimum of 37 degrees C and required magnesium ions for enzyme activity. Thus, it has been demonstrated unequivocally that VP1 represents the RdRp of IBDV.
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