|Original language||English (US)|
|Title of host publication||Encyclopedia of Biophysics|
|Editors||Gordon C K Roberts|
|Publisher||Springer Berlin Heidelberg|
|Number of pages||7|
|State||Published - 2013|
Topoisomerases are enzymes that modify the topology of DNA inside the cell. They are present in all three domains of life and are involved in several cellular processes, such as transcription, replication, and recombination (Champoux 2001; Wang 2002). All topoisomerases operate by forming transient phosphotyrosine covalent bond(s) with either the 5′ or the 3′ end(s) of the broken DNA strand(s), followed by passage of the unbroken strand(s) through the break, and ultimately resealing the break(s) to change the DNA topology. Topoisomerases are classified into two types, type I and type II enzymes, based on whether they cleave a single strand (type I) or both strands (type II) of DNA. Type I enzymes use the energy stored in supercoiled DNA as torsional strain for driving the DNA relaxation reaction and do not require any high energy cofactor for their activity. Type II enzymes utilize ATP hydrolysis to drive conformational changes in the protein. The central role of topoisomerases in cellular processes is underscored by the fact that they are the target of several chemotherapeutic agents and antibiotics (Pommier et al. 2010).