Restriction Enzyme

Restriction Enzymes or Restriction Endonucleases are enzymes that cut DNA at or near specific recognition DNA sequences known as restriction sites. They are essential tools in molecular biology. In 1970, American microbiologists Daniel Nathans and Hamilton O. Smith discovered the first type II restriction enzymes and were awarded the Nobel Prize in Physiology or Medicine in 1978 for their discovery.

History

The concept of restriction enzymes originated from studies of Escherichia coli (E. coli) in the 1950s. Werner Arber, a Swiss microbiologist, discovered that certain strains of E. coli have an unusual method of viral defense. This defense mechanism involves the production of enzymes that can cleave viral DNA; these enzymes are called restriction enzymes.

Types

There are four main types of restriction enzymes: Type I, Type II, Type III, and Type IV. Each type has a different mechanism of action.

Type I

Type I restriction enzymes cleave DNA at random locations that can be a considerable distance away from their recognition sequences.

Type II

Type II restriction enzymes are the most commonly used type in molecular biology. They cleave DNA at specific short sequences.

Type III

Type III restriction enzymes cleave DNA some distance away from their recognition sequences.

Type IV

Type IV restriction enzymes target modified DNA, such as methylated, hydroxymethylated or glucosylated DNA.

Applications

Restriction enzymes have many applications in molecular biology. Some of these include DNA cloning, DNA mapping, and DNA sequencing. They are also used in genetic engineering to insert genes into plasmids, which are then inserted into bacteria to produce proteins.

See Also

• DNA Sequencing
• Genetic Engineering
• Molecular Biology

References

Restriction Enzyme Resources
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