The VP2 protein of grass carp reovirus(GCRV) expressed in a baculovirus exhibits RNA polymerase activity

The double-shelled grass carp reovirus(GCRV) is capable of endogenous RNA transcription and processing. Genome sequence analysis has revealed that the protein VP2, encoded by gene seg-ment 2(S2), is the putative RNA-dependent RNA polymerase(RdRp). In previous work, we have ex-pressed the functional region of VP2 that is associated with RNA polymerase activity(denoted as rVP2390-900) in E. coli and have prepared a polyclonal antibody against VP2. To characterize the GCRV RNA polymerase, a recombinant full-length VP2(rVP2) was first constructed and expressed in a baculovirus system, as a fusion protein with an attached His-tag. Immunofluorescence(IF) assays, together with immunoblot(IB) analyses from both expressed cell extracts and purified His-tagged rVP2, showed that rVP2 was successfully expressed in Sf9 cells. Further characterization of the replicase activity showed that purified rVP2 and GCRV particles exhibited poly(C)-dependent poly(G) polymerase activity. The RNA enzymatic activity required the divalent cation Mg2+, and was optimal at 28 °C. The results provide a foundation for further studies on the RNA polymerases of aquareoviruses during viral transcription and replication.