Stretching and relaxation curves for λ-DNA and various combinations of UvsY, gp32 and *I in 10 mM Hepes,100 mM Na+ (95mM NaCl and 5mM NaOH) and pH 7.5. Data are shown in the absence of protein (dark blue), 200 nM gp32 (red), 200 nM gp32 and 100nM UvsY (pink open diamonds), 200nM *I (blue), and 200 nM of *I and 100 nM UvsY (green solid diamonds). The time for stretching and relaxation is approximately two minutes. The reproducibility of these measurements for individual stretching curves is similar to that obtained for the data in Fig. 3.