Suppressed Stops and Surreptitious Starts: G-Quadruplex-Guided Translation in the 3′ Untranslated Region

Abstract

Several non-canonical translation events can lead to the generation of multiple protein isoforms from a single transcript, challenging the long-held notion that eukaryotic mRNAs are monocistronic. Advances in techniques such as ribosome profiling and mass spectrometry have provided evidence for translation occurring outside the annotated coding sequence of mRNAs. Some non-canonical translation events occur in the 3′ untranslated regions (3′UTRs) of mRNAs. Phenomena such as stop codon readthrough (SCR, the recoding process by which ribosomes continue translation beyond a stop codon), and translation of short downstream open reading frames (dORFs) contribute to translation events in the 3′UTRs. G-quadruplex (G4) structures are non-canonical structures formed by G-rich elements. G4s are known to regulate diverse aspects of the mRNA life cycle, including transcription, splicing, poly-adenylation, mRNA transport, as well as translation. The current study aimed to identify non-canonical translation events in the 3′UTR of mammalian mRNAs driven by G-quadruplex (G4) structures. The first part of this thesis provides an introduction to all these phenomena. The second part of this thesis focuses on the identification of a dORF in the 3′UTR of MAP3K10; translation from which is driven by a G4 structure. The third part of this work delineates the mechanism of SCR in MPZ that involves a G4 structure we characterized in the 3′UTR. The fourth part of this thesis focuses on a therapeutic application of SCR- induction of SCR across Duchenne muscular dystrophy (DMD)-causing nonsense mutations