Structure of an RNA G-quadruplex from the West Nile virus genome.

Potential G-quadruplex sites have been identified in the genomes of DNA and RNA viruses and proposed as regulatory elements. The genus Orthoflavivirus contains arthropod-transmitted, positive-sense, single-stranded RNA viruses that cause significant human disease globally. Computational studies have identified multiple potential G-quadruplex sites that are conserved across members of this genus. Subsequent biophysical studies established that some G-quadruplexes predicted in Zika and tickborne encephalitis virus genomes can form and known quadruplex binders reduced viral yields from cells infected with these viruses. The susceptibility of RNA to degradation and the variability of loop regions have made structure determination challenging. Despite these difficulties, we report a high-resolution structure of the NS5-B quadruplex from the West Nile virus genome. Analysis reveals two stacked tetrads that are further stabilized by a stacked triad and transient noncanonical base pairing. This structure expands the landscape of solved RNA quadruplex structures and demonstrates the diversity and complexity of biological quadruplexes. We anticipate that the availability of this structure will assist in solving further viral RNA quadruplexes and provides a model for a conserved antiviral target in Orthoflavivirus genomes.

One primer to rule them all: universal primer that adds BBa_B0034 ribosomal binding site to any coding standard 10 BioBrick.

Here, we present a universal, simple, efficient, and reliable way to add small BioBrick parts to any BioBrick via PCR that is compatible with BioBrick assembly standard 10. As a proof of principle, we have designed a universal primer, rbs_B0034, that contains a ribosomal binding site (RBS; BBa_B0034) and that can be used in PCR to amplify any coding BioBrick that starts with ATG. We performed test PCRs with rbs_B0034 on 31 different targets and found it to be 93.6% efficient. Moreover, when supplemented with a complementary primer, addition of RBS can be accomplished via whole plasmid site-directed mutagenesis, thus reducing the time required for further assembly of composite parts. The described method brings simplicity to the addition of small parts, such as regulatory elements to existing BioBricks. The final product of the PCR assembly is indistinguishable from the standard or 3A BioBrick assembly.