Is an RNA-dependent RNA polymerase active in viral RNA replication. Is a methyltransferase active in RNA capping and an RNA helicase. Methyltransferase displays a cytoplasmic capping enzyme activity. This function is necessary since all viral RNAs are synthesized in the cytoplasm, and host capping enzymes are restricted to the nucleus. Helicase region probably exhibits NTPase and RNA unwinding activities (Potential). It also acts as a suppressor of RNA-mediated gene silencing, also known as post-transcriptional gene silencing (PTGS), a mechanism of plant viral defense that limits the accumulation of viral RNAs. May mediate silencing suppression through either inhibition of HEN1-mediated siRNA or siRNA demethylation (By similarity). a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) ATP + H2O = ADP + H(+) + phosphate Heterodimer of a large and a small subunit. This protein is translated as a fusion protein by episodic readthrough of a termination codon. When readthrough of the terminator codon TGA occurs between the codons for Gln-1116 and Gln-1118, this results in the addition of the RdRp region to the replicase. Belongs to the ssRNA positive-strand viruses RNA-directed RNA polymerase family.