RNA-dependent RNA polymerase replicates the viral genome composed of 2 RNA segments, RNA1 and RNA2. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) ATP + H2O = ADP + H(+) + phosphate The replicase 1a is produced from conventional translation of the 1a ORF. The replicase 1ab is generated probably by a +1 ribosomal frameshifting mechanism occurring at the 1a-1b genes boundary. The C-terminal domain is required for autoproteolysis. Belongs to the ssRNA positive-strand viruses RNA-directed RNA polymerase family.