RNA-dependent RNA polymerase, which is responsible for the replication and transcription of the viral RNA genome. 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 heterogeneous and not polyadenylated. The replicase function is to direct synthesis of antigenomic and genomic RNA which are encapsidated and non capped. As a consequence of the use of the same enzyme for both transcription and replication, these mechanisms need to be well coordinated. These processes may be regulated by proteins N and Z in a dose-dependent manner. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) For endonuclease activity. Binds 2 Mn(2+) ions in the active site (By similarity). The divalent metal ions are crucial for catalytic activity (By similarity). For polymerase activity. Homomultimer; the oligomeric structure is essential for the polymerase activity. Interacts with nucleoprotein N (By similarity). Interacts with protein Z; this interaction inhibits viral transcription and replication (By similarity). The N-terminus contains the endonuclease activity (endoN). The central region contains the RdRp activity. Classified as His(-) endonuclease since it does not have a histidine upstream of the active site that coordinates the first cation. His(-) endonucleases display very low activity in vitro, although they are clearly active in vivo. Belongs to the Arenaviridae RNA polymerase family.