The MYC G-quadruplex (G4) impedes λ-exo digestion. (A) Diagram of the plasmid digestion experiment. The predicted sizes of single-stranded fragments resulting from the inability of λ-exo to digest through the G4 motifs are shown. (B) Digestion of 3′-labeled BglII linearized pFRT.myc6xERE in glycine-KOH (pH 9.4). Double-stranded and single-stranded DNA were used as indicated. (C) Digestion of single-stranded DNA from pFRT.myc6xERE and deletion mutants of Pu30 and Pu27 in four different buffers. The pH of the buffer and the base used to titrate the pH are indicated.