VP1 of infectious bursal disease virus is an RNA-dependent RNA polymerase

von Einem, U.I.; Gorbalenya, A.E.; Schirrmeier, Horst GND; Behrens, S.V.; Letzel, Tobias GND; Mundt, Egbert GND

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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von Einem, U.I. / Gorbalenya, A.E. / Schirrmeier, Horst / et al: VP1 of infectious bursal disease virus is an RNA-dependent RNA polymerase. 2004.

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