VP1 of infectious bursal disease virus is an RNA-dependent RNA polymerase.
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.
Institute of Molecular Biology, Federal Research Centre for Viral Diseases of Animals, Boddenblick 5a, 17493 Greifswald-Insel Riems, Germany.
Ursula I
UI
von Einem
Department of Medical Microbiology, Center of Infectious Diseases, Leiden University Medical Center, Postbus 9600, 2300 RC Leiden, The Netherlands.
Alexander E
AE
Gorbalenya
Institute for Diagnostic Virology, Federal Research Centre for Viral Diseases of Animals, Boddenblick 5a, 17493 Greifswald-Insel Riems, Germany.
Horst
H
Schirrmeier
Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, PA 19111, USA.
Sven-Erik
SE
Behrens
Institute of Molecular Biology, Federal Research Centre for Viral Diseases of Animals, Boddenblick 5a, 17493 Greifswald-Insel Riems, Germany.
Tobias
T
Letzel
Institute of Molecular Biology, Federal Research Centre for Viral Diseases of Animals, Boddenblick 5a, 17493 Greifswald-Insel Riems, Germany.
Egbert
E
Mundt
D000818:Animals; D002384:Catalysis; D012367:RNA, Viral / Q000096:biosynthesis; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism*; D018411:Spodoptera; D015678:Viral Structural Proteins / Q000378:metabolism*
D012367:RNA, Viral; C107669:VP1 protein, infectious bursal disease virus; D015678:Viral Structural Proteins; D012324:RNA-Dependent RNA Polymerase