Figure 1.

Py25 and its modifications can fold into i-motif structures.A, the promoter sequences of NHE III₁ and its modifications. Py25 indicates the 25-nt core of the C-rich NHE III₁ promoter containing 5 runs of cytosines, as marked in red. Py25(1245) and Py25(1234) contain four runs of cytosines, which are indicated in the parentheses. B, a schematic representation of the C:C⁺ base pair (top) and the topological structures of type-1245 and type-1234 (bottom). C, CD spectra of Py25, Py25(1245), and Py25(1234) at different pH levels from 5.2 to 8.0, including 200 mM K⁺, 40% PEG200 (w/v), and 4 mM Trolox. Under pH 5.8, all three substrates could fold into i-motif structures, showing a positive peak at ∼287 nm and a negative peak at ∼262 nm. NHE, nuclear hypertensive element.