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). ATP + H2O = ADP + H(+) + phosphate a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Heterodimer of a large and a small subunit. The replicase large subunit 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 1187-Lys and 1189-Arg, this results in the addition of the RdRp region. Belongs to the ssRNA positive-strand viruses RNA-directed RNA polymerase family.