Development of RNA G-quadruplex (rG4)-targeting L-RNA aptamers by rG4-SELEX.

RNA G-quadruplex (rG4)-SELEX is a method that generates L-RNA aptamers to target an rG4 structure of interest, which can be applied to inhibit G-quadruplex-mediated interactions that have important roles in gene regulation and function. Here we present a Protocol Extension substantially modifying an existing SELEX protocol to describe in detail the procedures involved in performing rG4-SELEX to identify rG4-specific binders that can effectively suppress rG4-peptide and rG4-protein associations. This Protocol Extension improves the speed of aptamer discovery and identification, offering a suite of techniques to characterize the aptamer secondary structure and monitor binding affinity and specificity, and demonstrating the utility of the L-RNA aptamer. The previous protocol mainly describes the identification of RNA aptamers against proteins of interest, whereas in this Protocol Extension we present the development of an unnatural RNA aptamer against an RNA structure of interest, with the potential to be applicable to other nucleic acid motifs or biomolecules. rG4-SELEX starts with a random D-RNA library incubated with the L-rG4 target of interest, followed by binding, washing and elution of the library. Enriched D-aptamer candidates are sequenced and structurally characterized. Then, the L-aptamer is synthesized and used for different applications. rG4-SELEX can be carried out by an experienced molecular biologist with a basic understanding of nucleic acids. The development of rG4-targeting L-RNA aptamers expands the current rG4 toolkit to explore innovative rG4-related applications, and opens new doors to discovering novel rG4 biology in the near future. The duration of each selection cycle as outlined in the protocol is ~2 d.