This G4-forming sequence is composed of a polypurine/polypyrimidine tract that can transition from duplex to quadruplex DNA structure in vivo (25) and has been implicated in c-myc gene regulation in normal and cancer cells (Figure 1A).Given that this G4-forming sequence localizes near the most frequent translocation hot spot for the c-myc gene in B-cell malignancies, it is particularly relevant for studying mechanisms of mutagenesis (26–28). The gene discussed is MYC; the disease is cancer.