Resistance to a class of antibiotics targeting these enzymes often disrupts a water–metal ion bridge that chelates the drug’s keto acid. One of these enzymes from the vaccinia virus modifies a 3-prime thymidine in a namesake cloning method. An inhibitor of these enzymes was isolated (-5[1])from the barks of Camptotheca (-5[1])trees, derivatives (-5[2])of which (10[1])include (-5[1])irinotecan and a related drug (10[2])partially named after them. These enzymes create a “gate” for the T-segment to cross in (10[1])the “strand passage” mechanism. (10[2])Ciprofloxacin (-5[1])(“sip-ro-flox-uh-sin”) and other fluoroquinolones (“fluoro-quino-lones”) target (10[1])these enzymes, (-5[1])which can resolve catenanes. (-5[1])Bacteria use a type of these (10[1]-5[2])enzymes called gyrase (10[3])that generates (10[2])negative supercoils (10[2]-5[1])and changes (10[1])the linking (10[1])number (10[3]-5[2])by (10[1])two. (10[4]-5[2])For 10 points, (-5[2])name these enzymes (10[1])that relieve (10[1])torsional (-5[3])stress (10[1]-5[3])in DNA. (10[1])■END■ (10[14]0[35])