A strand of DNA can be bent into a tiny circle without snapping but only if it is twisted to a very specific tightness.
DNA is often thought of as a stiff ladder, but it is actually remarkably flexible under the right conditions. This research found that DNA can bend to a radius of just 3 nanometers without kinking or breaking. This flexibility only exists when the helical repeat is exactly 11 base pairs per turn. This sweet spot of twisting allows the molecule to handle extreme mechanical stress within a cell. Understanding this mechanical limit changes how we look at how genes are packed and accessed by biological machinery.
Twist-Dependent Elastic Limits and Unwinding of Tightly Bent DNA
bioRxiv · 2024.02.14.579968
DNA is under high bending and torsional strain in many biological contexts, but elastic limits of tightly bent DNA under simultaneous torsional strain are not fully understood. 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