A Chemical Probe Based on the PreQ1 Metabolite Enables Transcriptome-wide Mapping of Binding Sites

Abstract The role of metabolite-responsive riboswitches in regulating gene expression in bacteria is well known and makes them useful systems for the study of RNA-small molecule interactions. Here, we study the PreQ1 riboswitch system, assessing sixteen diverse PreQ1-derived probes for their ability to selectively modify the riboswitch aptamer covalently. For the most active probe, a diazirine-based photocrosslinker, X-ray crystallography and gel-based competition assays demonstrated the mode of binding of the ligand to the aptamer, and functional assays demonstrated that the probe retains activity against the full riboswitch. Transcriptome-wide mapping using Chem-CLIP revealed a highly selective interaction between the bacterial aptamer and the small molecule. In addition, a small number of RNA targets in endogenous human transcripts were found to bind specifically to PreQ1, providing evidence for candidate PreQ1 aptamers in human RNA. This work demonstrates a stark influence of linker chemistry and structure on the ability of molecules to crosslink RNA, reveals that the PreQ1 aptamer/ligand pair are broadly useful for chemical biology applications, and provides insights into how PreQ1 interacts with human RNAs.