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A restriction enzyme or restriction endonuclease is a special type of biological macromolecule that functions as part of the "immune system" in bacteria. One special kind of restriction enzymes is the class of "homing endonucleases", these being present in all three domains of life, although their function seems to be very different from one domain to another. The classical restriction enzymes cut up, And hence render harmless, any unknown (non-cellular) DNA that enters a bacterial cell As a result Of a viral infection. They recognize a specific DNA sequence, usually Short (3 To 8 bp), And cut it, producing either blunt Or overhung ends, either at Or nearby the recognition site. Restriction enzymes are quite variable In the Short DNA sequences they recognize. An organism often has several different enzymes, Each specific To a distinct Short DNA sequence.[1]
Enzyme
01 Syntax
02 Properties
| Name | Overloads | Summary |
|---|---|---|
| Enzyme | 1 | Accepted name of the molecule, according to the internationally adopted nomenclature[2][3], and bibliographical references. |
| PDB | 1 | Code used to identify the structure of a protein in the PDB database of protein structures. |
| Source | 1 | Organism that naturally produces the enzyme. |
| Recognition | 1 | Sequence of DNA recognized by the enzyme and to which it specifically binds. |
| Cut | 1 | Cutting site and DNA products of the cut. |
| Isoschizomers | 1 | Isoschizomers are pairs of restriction enzymes specific to the same recognition sequence. |
03 Members
Accepted name of the molecule, according to the internationally adopted nomenclature[2][3], and bibliographical references. (Further reading: see the section "Nomenclature" in the article "Restriction enzyme".)
Code used to identify the structure of a protein in the PDB database of protein structures. The 3D atomic structure of a protein provides highly valuable information to understand the intimate details of its mechanism of action[4][5].
Organism that naturally produces the enzyme.
Sequence of DNA recognized by the enzyme and to which it specifically binds.
Cutting site and DNA products of the cut. The recognition sequence and the cutting site usually match, but sometimes the cutting site can be dozens of nucleotides away from the recognition site[6][7]. (对所识别的位点Enzyme.Recognition的剪切的模式)
Isoschizomers are pairs of restriction enzymes specific to the same recognition sequence. For example, SphI (CGTAC/G) and BbuI (CGTAC/G) are isoschizomers of each other. The first enzyme discovered which recognizes a given sequence is known as the prototype; all subsequently identified enzymes that recognize that sequence are isoschizomers. Isoschizomers are isolated from different strains of bacteria and therefore may require different reaction conditions. An enzyme that recognizes the same sequence but cuts it differently Is a neoschizomer. Neoschizomers are a specific type (subset) Of isoschizomer. For example, SmaI (CCC/GGG) And XmaI (C/CCGGG) are neoschizomers Of Each other. An enzyme that recognizes a slightly different sequence, but produces the same ends Is an isocaudomer. In some cases, only one out of a pair of isoschizomers can recognize both the methylated as well as unmethylated forms of restriction sites. In contrast, the other restriction enzyme can recognize only the unmethylated form of the restriction site. This property of some isoschizomers allows identification of methylation state of the restriction site while isolating it from a bacterial strain. For example, the restriction enzymes HpaII And MspI are isoschizomers, as they both recognize the sequence 5'-CCGG-3' when it is unmethylated. But when the second C of the sequence is methylated, only MspI can recognize it while HpaII cannot.