RNA-dependent RNA polymerase, which is responsible for the replication and transcription of the viral RNA genome using antigenomic RNA as an intermediate. During transcription, synthesizes subgenomic RNAs and assures their capping by a cap-snatching mechanism, which involves the endonuclease activity cleaving the host capped pre-mRNAs. These short capped RNAs are then used as primers for viral transcription. The 3'-end of subgenomic mRNAs molecules are not polyadenylated. During replication, the polymerase binds the 5' and 3' vRNA extremities at distinct sites. In turn, significant conformational changes occur in the polymerase and in vRNA to initiate active RNA synthesis. As a consequence of the use of the same enzyme for both transcription and replication, these mechanisms need to be well coordinated 