Figure 1.

Principle of the phased τ ratio approach. (A) RNA molecules (heteroduplex; htx) with single bends have shorter birefringence decay times (τ) than a linear (duplex; dplx) control, for either fixed (θ_o) or flexible (〈θ〉_rms) interstem angles, because the heteroduplex is less extended in solution. The resulting single-bend τ ratio, τ_htx/τ_dplx, does not generally provide a measure of the range (dispersion) of the angle (8). (B) RNA molecules with two bends in various torsional alignments (phasings) will display τ ratios that are dependent on the additional flexibility of the bends. Double-bend constructs can thus be used in conjunction with single-bend (mean) angles to estimate the effective bend dispersion. 〈θ〉_rms = 〈θ²〉½, where θ is the total instantaneous angle.