Figure 1.

Observing the folded and unfolded states of 113 nt h22L ssDNA using the TPM method. (a) Our experimental geometry contains human telomeric sequence AGGG(TTAGGG)₃ and 48 nt AC copolymer (no secondary structure). DNA is immobilized on the surface with a streptavidin-decorated polystyrene bead (200 nm) attached on the other end as a reporter. (b) Histogram of the BM amplitude of h22L under the folded-state condition (150 mM NaCl). Gaussian fitting returns the peak at 12.75 ± 2.62 nm (±σ) (N = 144). (c) BM histogram of h22L interacting with 12 nt, antisense c12 DNA. The peak at 24.52 ± 5.40 nm (N = 44) is assigned to the unfolded state. (d) BM histogram of h22L with noncomplementary sequence t16. The peak stays at the folded state, 10.80 ± 3.00 nm (N = 30). (e) BM histogram of h22L at 100 mM KCl condition with the peak at the folded state, 12.30 ± 3.15 nm (N = 67).