Restriction enzyme, endonuclease

Restriction Enzyme

A restriction enzyme, also known as a restriction endonuclease, is a protein produced by bacteria that cleaves DNA at specific sites along the molecule. In the bacterial cell, restriction enzymes cleave foreign DNA, thus eliminating infecting organisms. They are a crucial tool in molecular biology, particularly in the field of genetic engineering.

History

The discovery of restriction enzymes was a pivotal moment in molecular biology. The first restriction enzyme was isolated in the 1960s by Werner Arber, Hamilton O. Smith, and Daniel Nathans, who were awarded the Nobel Prize in Physiology or Medicine in 1978 for their work. Their discovery allowed for the development of recombinant DNA technology, which has had profound implications for genetics, medicine, and biotechnology.

Mechanism of Action

Restriction enzymes recognize specific, short nucleotide sequences in DNA, known as recognition sites, and cleave the DNA at or near these sites. The sequences are typically palindromic, meaning they read the same forward and backward. For example, the recognition site for the enzyme EcoRI is GAATTC.

There are three main types of restriction enzymes:

• Type I enzymes cleave DNA at random sites far from their recognition sequences.
• Type II enzymes cleave DNA at specific sites within or near their recognition sequences. These are the most commonly used in laboratories.
• Type III enzymes cleave DNA at sites a short distance from their recognition sequences.

Applications

Restriction enzymes are indispensable tools in molecular cloning, genetic mapping, and DNA sequencing. They are used to cut DNA into smaller fragments, which can then be separated and analyzed. This is essential for recombinant DNA technology, where DNA from different sources is combined to create new genetic combinations.

In genetic engineering, restriction enzymes are used to insert genes into plasmids, which can then be introduced into bacteria or other host cells. This allows for the production of proteins, such as insulin, on a large scale.

Also see

• DNA ligase
• Polymerase chain reaction
• Gel electrophoresis
• Recombinant DNA
• Genetic engineering

References

• Arber, W. (1974). "DNA modification and restriction." Progress in Nucleic Acid Research and Molecular Biology.
• Smith, H.O., & Nathans, D. (1973). "A suggested nomenclature for bacterial host modification and restriction systems and their enzymes." Journal of Molecular Biology.