Restriction endonuclease

Restriction endonucleases, also known as restriction enzymes, are proteins that cleave DNA at specific sequences. They are produced by bacteria as a defense mechanism against viruses, and are widely used in molecular biology.

History

The discovery of restriction endonucleases was a key event in the development of molecular biology. They were first observed in the early 1950s, when researchers noticed that some strains of Escherichia coli were resistant to infection by certain bacteriophages. This resistance was due to the bacteria's ability to degrade the phage DNA, a process that was later found to be mediated by restriction endonucleases.

Classification

Restriction endonucleases are classified into four types (Type I, II, III, and IV) based on their structure, cofactor requirements, and the nature of their recognition sequence. Type II restriction endonucleases, which recognize specific short sequences of DNA and cleave at precise locations within or near these sequences, are the most commonly used in molecular biology.

Mechanism of action

Restriction endonucleases recognize specific sequences of DNA, known as restriction sites, and cleave the DNA at these sites. The recognition sequences are usually 4-8 base pairs in length, and are often palindromic, meaning they read the same forwards and backwards. The enzymes cleave the DNA by breaking the phosphodiester bonds between the nucleotides.

Applications

Restriction endonucleases have many applications in molecular biology. They are used in cloning to cut DNA into fragments that can be inserted into plasmids, in DNA sequencing to generate fragments of DNA that can be sequenced, and in genetic engineering to introduce specific changes into the DNA of organisms.

See also

• DNA sequencing
• Genetic engineering
• Molecular cloning

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