(a) Schematic of the human PDGFR-β gene promoter and the formation of a dGMP-fill-in vG4 as well as the berberine–dGMP–vG4 ternary complex. The vG4-forming region of the NHE sequence and its modifications are shown. The guanine residues involved in the formation of the fill-in vG4 are colored in red and mutations in cyan, respectively. (b) 1D 1H NMR spectra of dGMP–Pu19m2 DNA in the absence and presence of berberine with complete imino proton assignment. Conditions: 1.5 mM Pu19m2 DNA, 3:1 dGMP/DNA, 2:1 drug/DNA, pH 7, 50 mM K+ solution, 25 °C. (c) Chemical structure of berberine with numbering.