Journal of General Virology

Fig. 5. Model to show the effect of nascent chain assembly on vRNAP processivity during replication. In this model, the nucleocapsid template is depicted as a linear assembly of 'lego-like' N protein subunits, each containing six nucleotides. vRNAP is depicted as a large oval containing an active site (white circle). In this schema, the template and nascent chain are fixed and only vRNAP moves. The transcription elongation complex, in the middle, has two choices at each template position. The complex can either add the next nucleotide to the nascent chain and move forward (top) or backtrack along the template and nascent RNA, breaking the nascent chain-template base pairs on the downstream side and reforming an equal number of base pairs on the upstream side, thus causing a pause in RNA synthesis (bottom). Note that vRNAP backtracking requires the recently exposed nascent RNA chain to re-enter the RNA exit channel, which is prevented when this chain is already assembled with N subunits. The prevention of RNAP backtracking thus promotes RNAP processivity during genome replication by eliminating pausing.

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