Measuring G-quadruplex and R-loop formation in transcription and translation.
Single Molecule and Single Cell Imaging, Department of Biophysics, The Johns Hopkins University.
G-qudruplex (G4) is a noncanonical secondary structure that can form in both DNA and RNA. Human genome contains over 400,000 potential G4 forming sequences (PQS) and they are highly enriched in upstream of oncogene promoters and regulatory genes, strongly suggesting a switch-like function with programed positioning. Many previous studies have demonstrated the role of G4 in up or downregulating genomic processes including replication, transcription and translation. Our recent study demonstrated that in transcription, G4 forming sequence located in the non-template strand leads to a robust formation of R-loop (mRNA annealed to template strand), which in turn, induces G4 structure in the non-template strand. Remarkably, such R-loop/G4 structure drives enhanced transcription by a mechanism that involves successive formation and release of R-loop. Furthermore, we demonstrate that 5’UTR-G4 bearing mRNA (RG4) leads to over 10-fold enhanced translation in a cell-free system and in e.coli cells. Upon testing several plausible hypotheses, we propose that the RG4 structure promotes translation by blocking ribosomes from sliding off the mRNA. Our study reveals the structure-function relationship of how G4 and R-loop regulates transcription and translation activity.