Table 1.
Free energy (ΔGtotal) and cooperativity (σ) of the helix-coil transition of a single λ-DNA molecule as a function of ionic strength in the absence of protein and in the presence of 7 nM SSHS NC or wild-type (wt) NC
| Ionic strength, mM | No NC
|
SSHS
NC
|
wt NC
|
|
|---|---|---|---|---|
| ΔGtotal, kcal/mol⋅bp | ΔGtotal, kcal/mol⋅bp | ΔGtotal, kcal/mol⋅bp | σ | |
| 150 | 1.5 ± 0.1 | 1.5 ± 0.1 | 1.5 ± 0.1 | 0.001 |
| 100 | 1.5 ± 0.1 | 1.4 ± 0.1 | 1.4 ± 0.1 | 0.001 |
| 75 | 1.4 ± 0.1 | 1.4 ± 0.1 | 1.2 ± 0.3 | 0.05 |
| 50 | 1.3 ± 0.1 | 1.6 ± 0.1 | 0.6 ± 0.2 | 0.13 |
| 25 | 1.2 ± 0.1 | 1.6 ± 0.2 | 0.6 ± 0.1 | 0.25 |
Cooperativity results are shown only for wt NC, because this value remains essentially constant at 0.001 in the absence of NC or with SSHS NC. Reported error is calculated as the root mean square of the error due to reproducibility of the force measurement for at least three stretches and estimated error due to interpolation of ssDNA curves.