E.coli topoisomerase III
(I)contains a hole capable of holding duplex DNA that is lined with negatively charged residues.
(II)binds the sugar-phosphate backbone such that base recognition is possible.
(III)functions by nucleophilic attack on the binding phosphate group.

Question

Quizplus · Accepted Answer

Topoisomerase III binds to the sugar-phosphate backbone of duplex DNA to recognize the base. It then introduces a nucleophile to the binding phosphate group, which allows for DNA cleavage and rejoining. The hole in the enzyme is negatively charged and can hold duplex DNA. Therefore, statements II and III are accurate, making B the correct answer. However, statement I is not true as it is the site of nucleophilic attack, not a binding site for DNA.

E.coli Topoisomerase III (I)contains a Hole Capable of Holding Duplex DNA That Is