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That an entire 500bp would be protected from DNase seems very very strange - but very interesting if true! Could that band on the agarose gel be something else? Protein will stain a bit with ethidium as well as with coomassie. Did you add SDS before running the agarose gel or is it native (in which case the size of an intact protein-DNA complex is not directly related to the mobility, as others have noted)? How do the 280 and 260nm peaks in your UV spectrum compare to those expected for your protein (before adding ATP, and possibly expecting 1 ATP / molecule to come along for the ride during purification)? Good luck, Phoebe Rice ++++++++++++++++++++++++++++++++++++++++++ Phoebe A. Rice Dept. of Biochemistry & Molecular Biology The University of Chicago [log in to unmask]<mailto:[log in to unmask]> ________________________________