Fig. 3: Role of ROS in G4 formation and stability.

ROS oxidizes guanine in G4s and blocks the Hoogsteen hydrogen bonds, which disrupts the thermal stability of the G4 structure (a, b). The guanine bases in the surrounding G-rich region can compensate for the missing guanine and stabilize the G4 structure (a). In addition, G4 can also be modified into other structural forms by altering the G4-forming mode (c). Oxidation of the guanine base in the DNA template chain can also form OG. With the help of RNA polymerase, the RNA chain can form R-loop with the original DNA chain and stabilize the G4 structure (d).