A mechanistic model of de novo initiation and elongation of flavivirus genomic RNA, highlighting the critical events of genome circularization, NS5 dimerization, and UFS-mediated de novo initiation and elongation (see text for details). NS5 (green) bound to 5′ UTR (SLA and SLB) is well established by Gamarnik group (Filomatori et al. 2006, 2011; Lodeiro et al. 2009) and the present study showed the specific interaction between a molecule of NS5 (purple) through R888 at its carboxy-terminal region and the top-loop of 3′SL. Long-range RNA interactions within the open reading frame region (Huber et al. 2019) juxtaposes the 5′ and 3′ CS and DAR for RNA cyclization supported by NS5–RNA complex formation. The cis-acting tunable UFS region ensures primer-independent RNA replication by serving as a gate keeper to ensure the formation of a productive stable de novo initiation complex that can carry out processive RNA replication in concert with viral and host proteins.
