Figure 2.

CD spectra for G- and C-rich single oligonucleotide strands from the Gad1 promoter. A, C, WT and mutant oligonucleotides for analysis of the Gad1 promoter G-rich and C-rich strands, respectively. Yellow represents conserved G-quadruplex and i-motif consensus sequences. Red represents mutated positions. B, Spectra for the WT G-rich strand were potassium-dependent and consistent with G-quadruplex formation. By contrast, spectra for the mutant strand were not potassium-dependent, indicating that G-quadruplexes were not formed. D, Spectra for the WT C-rich strand were pH-dependent and consistent with i-motif formation. Spectra for the mutant strand did not show any pH dependence, indicating that i-motifs were not formed. By contrast, methylation of all cytosines in CpG motifs within the WT oligonucleotide enhanced the signal maxima of the spectra, indicating that methylation increased i-motif formation.