- Also called:
- restriction endonuclease
- Key People:
- Hamilton O. Smith
- Werner Arber
Restriction enzyme
-
What is a restriction enzyme?
A restriction enzyme is a protein produced by bacteria that cleaves DNA at specific sites along the molecule. In bacterial cells, restriction enzymes target foreign DNA, thus eliminating infecting organisms like bacteriophages. These enzymes are indispensable tools in recombinant DNA technology, also known as genetic engineering, for manipulating DNA fragments containing genes.
Each restriction enzyme recognizes a specific sequence of nucleotide bases called recognition sequences or sites, randomly distributed throughout the DNA. When a restriction endonuclease recognizes a sequence, it cuts the DNA molecule by catalyzing the hydrolysis of the bond between adjacent nucleotides.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What do restriction enzymes do in a cell?
Restriction enzymes are proteins produced by bacteria that cut DNA at specific sites, defending against foreign DNA from infecting organisms like bacteriophages. They recognize short, specific nucleotide base sequences randomly distributed throughout the DNA, called recognition sequences. The enzyme cuts the DNA molecule by catalyzing the hydrolysis of the bond between adjacent nucleotides. Bacteria protect their own DNA by modifying their recognition sequences using methylase enzymes, which add methyl groups to adenine or cytosine bases within the sequence. There are four types of restriction enzymes, each differing in structure, cleavage site, specificity, and cofactors.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Where are restriction enzymes found in nature?
Restriction enzymes are naturally produced by bacteria. Within the bacterial cell, these proteins serve to cleave foreign DNA, thereby eliminating infecting organisms such as bacteriophages. Each enzyme recognizes a specific, short sequence of nucleotide bases, known as recognition sites, on the DNA molecule and cuts the DNA at these sites.
Bacteria prevent the restriction enzymes from degrading their own DNA by disguising their recognition sequences using enzymes called methylases. The restriction enzyme and its corresponding methylase constitute the restriction-modification system of a bacterial species.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do restriction enzymes recognize specific DNA sequences?
Restriction enzymes, produced by bacteria, are proteins that cut DNA at particular locations on the molecule. They protect bacteria by cleaving foreign DNA, such as that of bacteriophages, preventing replication.
Each restriction enzyme identifies a short, specific sequence of nucleotide bases called recognition sequences or sites, which are scattered throughout the DNA. When a restriction endonuclease recognizes a sequence, it cuts the DNA molecule by catalyzing the hydrolysis of the bond between adjacent nucleotides. Bacteria prevent the degradation of their own DNA by disguising their recognition sequences using enzymes called methylases, which add methyl groups to adenine or cytosine bases within the recognition sequence, thus modifying and protecting it from the endonuclease.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What happens to DNA when a restriction enzyme cuts it?
Restriction enzymes are proteins that bacteria produce to cleave foreign DNA at specific sites, protecting themselves from infection. These enzymes, also called restriction endonucleases, recognize short nucleotide base sequences and cut the DNA molecule by catalyzing the hydrolysis of the bond between adjacent nucleotides.
There are four types of restriction enzymes (I, II, III, and IV), which differ in structure, specificity, cleavage site, and cofactors. Type II restriction enzymes precisely cleave DNA at specific sites within the recognition site, while Types I and III cut DNA randomly, sometimes far from the recognition sequence. Type IV restriction enzymes cleave only methylated DNA and show weak sequence specificity.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How are restriction enzymes used in genetic engineering or biotechnology?
Restriction enzymes are essential in genetic engineering for their ability to cleave DNA at specific sequences. These enzymes, found in bacteria, defend against bacteriophages by cutting foreign DNA into pieces.
In recombinant DNA technology, restriction enzymes act as "molecular scissors" to cut DNA into fragments, which are then inserted into DNA vectors such as plasmids or viruses. When donor and vector DNA are cut with the same restriction enzyme, the fragments can splice together due to complementary overhangs. DNA ligase then seals these segments, forming stable, recombinant DNA.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Restriction enzyme, 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. Restriction enzymes can be isolated from bacterial cells and used in the laboratory to manipulate fragments of DNA, such as those that contain genes; for this reason they are indispensible tools of recombinant DNA technology (genetic engineering).
A bacterium uses a restriction enzyme to defend against bacterial viruses called bacteriophages, or phages. When a phage infects a bacterium, it inserts its DNA into the bacterial cell so that it might be replicated. The restriction enzyme prevents replication of the phage DNA by cutting it into many pieces. Restriction enzymes were named for their ability to restrict, or limit, the number of strains of bacteriophage that can infect a bacterium.
Each restriction enzyme recognizes a short, specific sequence of nucleotide bases (the four basic chemical subunits of the linear double-stranded DNA molecule—adenine, cytosine, thymine, and guanine). These regions are called recognition sequences, or recognition sites, and are randomly distributed throughout the DNA. Different bacterial species make restriction enzymes that recognize different nucleotide sequences.
" height="20" alt="HEW Logo">
When a restriction endonuclease recognizes a sequence, it snips through the DNA molecule by catalyzing the hydrolysis (splitting of a chemical bond by addition of a water molecule) of the bond between adjacent nucleotides. Bacteria prevent their own DNA from being degraded in this manner by disguising their recognition sequences. Enzymes called methylases add methyl groups (—CH3) to adenine or cytosine bases within the recognition sequence, which is thus modified and protected from the endonuclease. The restriction enzyme and its corresponding methylase constitute the restriction-modification system of a bacterial species.
Traditionally, four types of restriction enzymes are recognized, designated I, II, III, and IV, which differ primarily in structure, cleavage site, specificity, and cofactors. Types I and III enzymes are similar in that both restriction and methylase activities are carried out by one large enzyme complex, in contrast to the type II system, in which the restriction enzyme is independent of its methylase. Type II restriction enzymes also differ from types I and III in that they cleave DNA at specific sites within the recognition site; the others cleave DNA randomly, sometimes hundreds of bases from the recognition sequence. Several thousand type II restriction enzymes have been identified from a variety of bacterial species. These enzymes recognize a few hundred distinct sequences, generally four to eight bases in length. Type IV restriction enzymes cleave only methylated DNA and show weak sequence specificity.
Restriction enzymes were discovered and characterized in the late 1960s and early 1970s by molecular biologists Werner Arber, Hamilton O. Smith, and Daniel Nathans. The ability of the enzymes to cut DNA at precise locations enabled researchers to isolate gene-containing fragments and recombine them with other molecules of DNA—i.e., to clone genes. The names of restriction enzymes are derived from the genus, species, and strain designations of the bacteria that produce them; for example, the enzyme EcoRI is produced by Escherichia coli strain RY13. It is thought that restriction enzymes originated from a common ancestral protein and evolved to recognize specific sequences through processes such as genetic recombination and gene amplification.