What Are Restriction Enzymes?

Restriction endonucleases are a class of enzymes that recognize and attach a specific deoxynucleotide sequence and cleave the phosphodiester bond between two deoxyribonucleotides at a specific position in each chain. Referred to as restriction enzymes. Restriction enzymes can be classified into three types according to the structure of restriction enzymes, the demand-cutting of cofactors, and the mode of action, which are Type I, Type II, and Type III ). Type I restriction enzymes can catalyze both methylation of host DNA and hydrolysis of unmethylated DNA; type II restriction enzymes only catalyze hydrolysis of unmethylated DNA. Type III restriction enzymes have both modification and cognitive cleavage effects.

Restriction endonuclease

Is to identify a specific nucleotide sequence between two nucleotides at a specific location in each strand

It is usually the first letter of the genus name and the first two letters of the species name

Restriction endonucleases are widely distributed, and at least one restriction enzyme is found in almost all genera and species of bacteria. Many of them have dozens of species in one genus, such as in Haemophilus Haemophilus) have been found in 22 species. some

Restriction endonucleases can be divided into two major categories, namely, type I enzymes and type II enzymes, according to their functional characteristics, size, and cofactors required for the reaction. The earliest EcoK and EcoB found in E. coli belong to class I enzymes. Its molecular weight is large; in addition to Mg ²⁺ during the reaction, S-

For DNA genome

Restriction enzymes are named according to the type of bacteria. Take EcoRI as an example:

E	Escherichia	(Genus)
co	coli	(Species)
R	RY13	(strain)
I	First found	The order in which such bacteria are found

Restriction enzymes can be classified into three types according to the structure of restriction enzymes, the demand cutting of cofactors, and the mode of action, which are Type I, Type II, and Type III. ).

Restriction is actually a protective mechanism that restricts the degradation of foreign DNA by enzymes and maintains the genetic stability of the host. Methylation is a common modification that protects methylation of adenine A and cytosine C. The purpose of identifying self genetic material and foreign genetic material is achieved through methylation. Therefore, a bacterium capable of producing a restriction enzyme that protects against virus infection may have a sequence recognized by the enzyme in its genome, but the recognition sequence or the restriction site is methylated. This is not to say that once methylated, all restriction enzymes cannot cleave. Most restriction enzymes are sensitive to DNA methylation, so when the target sequence of the restriction enzyme overlaps with the methylation site, there are 3 possible effects on the digestion, that is, no influence, partial influence, and complete prevention. The ability to cut methylated DNA is an inherent and unpredictable characteristic of restriction enzymes. Therefore, in order to effectively cut DNA, the sensitivity of DNA methylation and restriction enzymes to this type of methylation must be considered simultaneously. In addition, most commercial restriction enzymes are now dedicated to cleaving methylated DNA.