Topoisomerase

Topoisomerase is an enzyme that alters the supercoiling of double-stranded DNA. It is crucial in DNA replication and transcription, as it solves the problem of DNA supercoiling that occurs during these processes. There are two types of topoisomerases: Type I and Type II, which are further divided into subtypes.

Function

Topoisomerases are essential for the survival of the cell. They control and alter the topologic states of DNA by creating transient breaks in the DNA molecule and then rejoining them. This allows them to control the degree of supercoiling of the DNA, which is crucial during DNA replication and transcription.

Types

There are two types of topoisomerases: Type I and Type II.

Type I

Type I topoisomerases cut one strand of the DNA and relax the supercoiling. They are further divided into two subtypes: Type IA and Type IB.

Type IA

Type IA topoisomerases bind to single-stranded DNA and pass the other strand through the break.

Type IB

Type IB topoisomerases bind to double-stranded DNA and pass one strand through the break.

Type II

Type II topoisomerases cut both strands of the DNA and change the linking number by two in each enzymatic step. They are further divided into two subtypes: Type IIA and Type IIB.

Type IIA

Type IIA topoisomerases include the bacterial DNA gyrase and the eukaryotic topoisomerase II.

Type IIB

Type IIB topoisomerases include the archaeal topoisomerase VI.

Inhibitors

Topoisomerase inhibitors are used as chemotherapy agents. They work by stabilizing the topoisomerase-DNA cleavage complex, preventing the relegation step of the catalytic cycle which leads to the accumulation of DNA breaks.

See also

• DNA gyrase
• Topoisomerase inhibitor
• DNA supercoiling

Topoisomerase Resources
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