Round 3: Tossup 14

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 trees, derivatives of which include irinotecan and a related drug partially named after them. These enzymes create a “gate” for the T-segment to cross in the “strand passage” mechanism. Ciprofloxacin (“sip-ro-flox-uh-sin”) and other fluoroquinolones (“fluoro-quino-lones”) target these enzymes, which can resolve catenanes. (-5[1])Bacteria use a type of these enzymes called gyrase that generates (10[1])negative supercoils and changes the linking number by two. (10[1])For 10 points, name these enzymes that relieve torsional (-5[1])stress in DNA. ■END■ (0[3])

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