When DNA gyrase was isolated, Brown and Cozzarelli assessed its activity by gel electrophoresis
Relaxed DNA was shown to become increasingly supercoiled over time until all of the relaxed DNA at the top of the gel would run at the bottom of the gel. If the pattern of bands generated by DNA gyrase was compared to the pattern of a type I topoisomerase, how would they differ?
What will be an ideal response?
First, type I topoisomerases only relax supercoils, so the substrate of the reaction would have to be a supercoiled DNA that migrates at the bottom of the gel, and the action would form a pattern of bands that would move upward in position until all of the DNA would be relaxed and run at the top of the gel. Second, the ladder generated by gyrase would change linking numbers by two, and the type I topoisomerase would change by only one.
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