Folding and Persistence Time of Intramolecular G-Quadruplexes Transiently Embedded in a DNA duplex
G-quadruplex (G4) DNA structures have emerged as important regulatory elements during DNA replication, transcription or repair. While many in-vitro studies have focused on the kinetics of G4 formation within DNA single-strands, G4 are found in-vivo in double-stranded DNA regions, where their formation is challenged by pairing between the two complementary strands. Since the energy of hybridization of Watson-Crick structures dominates the energy of G4 folding, this competition should play a critical role on the persistence of G4 in vivo. To address this issue, we designed a single molecule assay allowing measuring G4 folding and persistence while the structure is periodically challenged by the complementary strand. We quantified both the folding rate and the persistence time of biologically relevant G4 structures and showed that the dynamics of G4 formation depends strongly on the genomic location. G4 are found much more stable in promoter regions and replication origins than in telomeric regions. In addition, we characterized how G4 dynamics was affected by G4 ligands and showed that both folding rate and persistence increased. Our assay opens new perspectives for the measurement of G4 dynamics, which is critical to understand their role in genetic regulation.