Figure 1.

CD spectra of d(CGA)-containing oligonucleotides. The positive band at 265 nm and negative band at 245 nm are characteristic of the ps-duplex form (Luteran et al., 2020 ▸; Kejnovská et al., 2001 ▸; Robinson & Wang, 1993 ▸). The antiparallel form has a weak positive band at 280 nm and a weak negative band at 260 nm (Luteran et al., 2020 ▸; Kejnovská et al., 2001 ▸; Robinson & Wang, 1993 ▸). (a) CD spectrum of GA(CGA)₅ at pH 5.5 (blue) or pH 7.0 (black). (b) CD spectrum of (CGA)₅TGA at pH 5.5 (blue) or pH 7.0 (black). (c) (CGA)₅ forms a ps-duplex at pH 5.0 (light blue) and an antiparallel hairpin at pH 6.6 (dark blue) in the same buffer conditions as in (a) and (b). The formation of the ps-duplex form at pH 6.6 is favored in the presence of 30% PEG 400 (dark gray), PEG 2000 (medium gray) and PEG 4000 (light gray). (d) Crowding agents increase the pH of the structural transition from ps-duplex to antiparallel hairpin form. The transition was measured as the loss of the characteristic ps-duplex signal at 265 nm in native conditions (solid lines) or in the presence of 30% PEG 2000 (dashed lines) for (CGA)₅ (gray) and (CGA)₅TGA (pink).