RNA-POLYMERASE ACTIVITY CATALYZED BY A POTYVIRUS-ENCODED RNA-DEPENDENT RNA-POLYMERASE

We have expressed the putative RNA-dependent RNA polymerase encoded by the potyvirus tobacco vein mottling virus (TVMV) in Escherichia coli as a glutathione S-transferase fusion protein. As prepared, the fusion protein possessed the poly(U) polymerase activity that is a hallmark of other picornavirus-encoded polymerases. In addition, this protein w as able to utilize full-length TVMV RNA as a template for RNA synthesi s. A fusion protein containing a mutation in the highly conserved GDD motif of the polymerase (GDD --> ADD) possessed 7% of the activity of the wild type. Our results confirm that the presumed polymerase encode d by TVMV is in fact an RNA-dependent RNA polymerase and that the GDD motif so widely seen in viral polymerases has an important function in the TVMV protein. (C) 1996 Academic Press, Inc.