Type I topoisomerase

Type I topoisomerase is a type of enzyme that functions to alter the supercoiling state of DNA. It is one of two main types of topoisomerase, the other being Type II topoisomerase.

Function

Type I topoisomerases function by creating a single-strand break in the DNA molecule, allowing the DNA to be untwisted or relaxed. This is achieved by the enzyme cleaving one strand of the DNA, passing the other strand through the break, and then resealing the break. This process is essential for various DNA processes such as replication, transcription, and recombination.

Mechanism

The mechanism of action of Type I topoisomerases involves the breaking and rejoining of single DNA strands. The enzyme binds to the DNA at a specific sequence, and then cleaves one of the strands. This creates a covalent bond between the enzyme and the DNA, which allows the other DNA strand to pass through the break. The enzyme then reseals the break, releasing the DNA in a less supercoiled state.

Types

There are two subtypes of Type I topoisomerases: Type IA and Type IB. Type IA topoisomerases change the linking number of DNA by increments of 1, while Type IB topoisomerases change the linking number by increments of 1 or -1.

Clinical significance

Type I topoisomerases are targets for several antibacterial and anticancer drugs. These drugs function by inhibiting the activity of the enzyme, leading to DNA damage and cell death. Examples of such drugs include camptothecin and its derivatives, which are used in the treatment of various types of cancer.

See also

• Type II topoisomerase
• DNA supercoiling
• DNA replication
• DNA transcription
• DNA recombination