The replicase large subunit is an RNA-dependent RNA polymerase active in viral RNA replication. The replicase small subunit is a methyltransferase active in RNA capping and an RNA helicase. 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. Readthrough of the terminator codon UAG occurs between codons for Gln-1103 and Gln-1105. Belongs to the tobamovirus RNA-directed RNA polymerase family.