English: The PV replication-elongation complexes for RNA dependent RNA polymerase. Sequential structures illustrating the movement of the different palm residues from a binary PV 3Dpol-RNA open complex (left) to an open 3Dpol-RNA-rNTP ternary complex (middle) where the incoming rNTP is positioned in the active site for catalysis and, a closed ternary complex (right) after nucleotide incorporation and pyrophosphate (PPi) release. The residues DA (involved in rNTP selection through an interaction with the 2′ hydroxyl group), DC (the catalytic aspartate of motif C), KD (the general acid residue of motif D that can coordinate the export of the PPi group) and NB (a conserved Asn of motif B, interacting with DA) have been highlighted as sticks. The different structures correspond to the 3Dpol-RNA (PDB id. 3OL6), 3Dpol-RNA-CTP open complex (PDB id. 3OLB) and 3Dpol-RNA-CTP closed complex (PDB id. 3OL7) structures of PV elongation complexes, respectively [7].