By Peter Weiss
Even when biophysicist Paul Wiggins pursues his favorite sport, rock climbing, he doesn’t leave his work behind. While struggling to untangle ropes—”one of the most frustrating aspects of climbing,” he says—Wiggins envisions great lengths of DNA tangled inside cells. The mechanical properties, particularly the flexibility, of that biomolecule fascinate him.
In cells, random thermal motion makes DNA and other long biomolecules wriggle. Experimenters have observed that the distance between bends in DNA tends to be around 50 nanometers. The stiffness of stretches shorter than that seems to overcome the thermal-bending forces. However, scientists have long known that short segments of DNA nonetheless become tightly curved in some cellular DNA-protein complexes, and researchers assumed that proteins muscle the DNA into those configurations. Until recently, however, researchers hadn’t looked directly at such short sections of DNA to see what they were actually doing.