1. Single-molecule analysis of DNA uncoiling by a type II topoisomerase Terence R. Strick, Vincent Croquette & David Bensimon 2-1-06, Katrine Rude Laub

2. Type II topoisomerases (topo2) plectoneme = interwound supercoil class of ATP-dependent enzymes that reduce supercoiling in DNA by breaking and rejoining both strands of the DNA molecule

3. Goals Follow in real time a single topo2 acting on linear DNA, which is mechanically stretched and supercoiled by a magnetic tweezer Monitore the extension of the DNA Directly observe the relaxation of two supercoils during a single catalytic turnover (ATP present) Determine the variation of the reaction rate with the applied stress Observe clamping of a DNA crossover by a single topo2 (ATP absent)

6. Michaelis-Menten kinetics E:= enzyme S:= substrate P:= product Reaction Michaelis-Menten equation Here