Figure 6.

Association in Mg²⁺. Equal volumes of Alexa-21 and a variant of the SfiI endonuclease, D79A (a) or D100A (b), were mixed in the stopped-flow fluorimeter to give reactions in Mg²⁺ fluorescence buffer at 25°C that contained 20 nM Alexa-21 and one of the following concentrations of SfiI protein (as indicated on the right): 12.5 nM, in red; 50 nM, in blue; 125 nM in fuchsia; 250 nM, in green. The increase in emission from Alexa-21, following Trp excitation was monitored with time and is shown in arbitrary units.