DNA topoisimerase

 DNA topoisomerase plays an impotant role in breaking the phosophodiester bond by binding covalently onto the DNA backbone phosphate. It acst as a reversible nuclease. This whole process is a reversible one, whereby before the protein leaves, the phosophodiester bonds are re-made. There are two types of DNA topoisomerase, topoisomerase I and topoismerase II.

Reference: 1. Alberts, BA, 2008. Molecular Biology of The Cell. 5th ed. New York: Garland Science.