Twist-Dependent Elastic Limits and Unwinding of Tightly Bent DNA

Abstract

DNA is under high bending and torsional strain in many biological contexts 1,2, but elastic limits of tightly bent DNA under simultaneous torsional strain are not fully understood 3-22. We synthesized DNA circles with all possible radii of curvature between r {approx} 2.7 - 5.7 nm in increments of{Delta} r = 0.05 nm and defined helical repeats ranging from h {approx} 10 - 13 base pairs per helical turn. Nuclease digest reveals that DNA can be bent to r {approx} 3.0 nm without kinking, but only when h 11 bp/turn due to twist-bend coupling, which is not caused by kinking before ligation. These findings require reassessing our models and the energetics of molecular mechanisms involving DNA under mechanical stress.