GSE173463
Flavivirus Capsid Proteins Facilitate Genome Compaction and Packaging
Dengue virus (DENV) and Zika virus (ZIKV) are single-stranded (+)-sense RNA viruses that infect humans and mosquitoes, posing a significant health risk in tropical and subtropical regions. Mature virions are composed of an icosahedral shell of envelope (E) and membrane (M) proteins circumscribing a lipid bilayer, which in turn contains a complex of the approximately 11 kb genomic RNA with capsid (C) proteins. Whereas the structure of the envelope is clearly defined, the structure of the packaged genome in complex with C proteins remains elusive. Here, we investigate the interactions of C proteins with viral RNA, in solution and inside mature virions, via footprinting and cross-linking experiments. We demonstrate that C protein interactions with DENV and ZIKV genomes saturate at an RNA:C protein ratio below 1:250, and that binding site lengths on the genome exhibit a bimodal distribution, suggesting that RNA-C protein complexes occur in singlets or pairs. We show that interaction sites are preferentially sites with low base pairing, as measured by previously measured SHAPE reactivity indicating structuredness. We found no preference for specific sequence motifs or nucleotide composition. However, RNA-C protein binding sites are strongly associated with long-range RNA-RNA interaction sites, particularly inside virions. This helps to explain the need of C protein for viral genome packaging: the protein could coordinate those key interactions, promoting proper packing of viral RNA. Such sites are thus possible targets for drug development strategies against these and related viruses. Overall design: footprinting and crosslinking experiments of flavivirus RNA with flavivirus capsid proteins