RT-qPCR as a screening platform for mutational and small molecule impacts on structural stability of RNA tertiary structures.

The exponential increase in the discovery and characterization of RNA tertiary structures has highlighted their active role in a variety of human diseases, yet often their interactome and specific function remain unknown. Small molecules offer opportunities to both decode these cellular roles and develop therapeutics, however there are few examples of small molecules that target biologically relevant RNA tertiary structures. While RNA triple helices are a particularly attractive target, discovery of triple helix modulators has been hindered by the lack of correlation between small molecule affinity and effect on structural modulation, thereby limiting the utility of affinity-based screening as a primary filtering method. To address this challenge, we developed a high-throughput RT-qPCR screening platform that reports on the effect of mutations and additives, such as small molecules, on the stability of triple helices. Using the 3'-end of the oncogenic long non-coding RNA MALAT1 as a proof-of-concept, we demonstrated the applicability of both a two-step and a one-pot method to assess the impact of mutations and small molecules on the stability of the triple helix. We demonstrated the adaptability of the assay to diverse RNA tertiary structures by applying it to the SARS-CoV-2 pseudoknot, a key viral RNA structure recently identified as an attractive therapeutic target for the development of antivirals. Employment of a functional high-throughput assay as a primary screen will significantly expedite the discovery of probes that modulate the structural landscape of RNA structures and, consequently, help gain insight into the roles of these pervasive structures.