Table 1. E2 site DNA curvature in solution.

Insert (N4)	E2 site net curvaturea (°)	Curvature directionb (bp)
1(AATT)	17.8 ± 1.2	22.26 ± 0.10
2(TTAA)	11.2 ± 2.5	22.42 ± 0.01
3 (ACGT)	1.2 ± 3.0	22.88 ± 0.06
4	0	22.45 ± 0.03

^aDNA curvature relative to insert 4. Curvature estimates were obtained as described in Materials and Methods. Curve fitting of phasing data to equation 2 allowed extraction of a phasing amplitude for each construct. Using phasing amplitudes for phased A₅ tract reference standards and an assumption of 18° curvature per A₅ tract, amplitudes were converted to degrees of DNA curvature. The reported E2 site curvature was obtained by subtracting the absolute curvature of insert 4 (∼28°) from curvature estimates for inserts 1–4. Data are averages ± standard deviations based on two experiments.

^bThe curvature direction is defined as the base pair spacing (arbitrary reference frame) separating the E2 test sequence in the insert duplex from the phased A₅ tract array in the right phasing arms, that gives rise to the minimum mobility (maximum curvature, hence maximal alignment of loci of curvature). For A₅ tract standards, this parameter has a value of 21.85 bp. The observation that this reference frame remains within ∼1 bp from the center of the E2 site indicates curvature in the expected direction. Deviation from the value of 21.85 bp observed for A₅ tracts can also reflect a subtle difference in the helical repeat parameter for the E2 binding sequence relative to the corresponding sequence in insert 4.