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. 2016 Jun 6;7:11810. doi: 10.1038/ncomms11810

Figure 6. Model for structural rearrangement of torsionally constrained DNA under tension.

Figure 6

At forces of ∼50–110 pN, the applied strain is sufficient to induce local regions of the molecule to form non-B-form underwound structures, namely bubble-melted (M) DNA and S-DNA at lower and higher ionic strengths, respectively. This is absorbed by the rest of the duplex which forms slightly overwound (+) B-DNA. At yet higher forces (∼110–130 pN) P-DNA becomes a viable overwound structure, enabling the rest of the molecule to form underwound structures (M/S-DNA). Note that, for simplicity, base-pairing is not shown in this schematic.