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 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, (-5[1])which can resolve catenanes. Bacteria use a type of these enzymes called gyrase that generates negative supercoils and changes (10[1])the linking number by two. For 10 points, (-5[1])name these enzymes that relieve torsional stress in DNA. ■END■ (10[1]0[2])

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