VP1 of infectious bursal disease virus is an RNA-dependent RNA polymerase von Einem, Ursula I. and Gorbalenya, Alexander E. and Schirrmeier, Horst and Behrens, Sven-Erik and Letzel, Tobias and Mundt, Egbert,, 85, 2221-2229 (2004), doi = https://doi.org/10.1099/vir.0.19772-0, publicationName = Microbiology Society, issn = 0022-1317, 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 °C and required magnesium ions for enzyme activity. Thus, it has been demonstrated unequivocally that VP1 represents the RdRp of IBDV., language=, type=