NEW MEASUREMENTS OF DNA TWIST ELASTICITY

The symmetries of the DNA double helix require a new term in its linea r response to stress: the coupling between twist and stretch. Recent e xperiments with torsionally constrained single molecules give the firs t direct measurement of this new material parameter. We extract its va lue from a recent experiment, Finally, we sketch the effect of constra ined twist on entropic elasticity of DNA arising from the connection b etween Link, Twist, and Writhe.