30 years ago, when people are restrictions on the phage host specificity – when modified to study the phenomenon , first discovered by restriction endonucleases . Bacteria can resist new viruses , and this ” limitation ” approach can be attributed to the survival of the virus inside the cell can destroy foreign DNA restriction endonucleases . The first restriction endonuclease from Escherichia coli is found to include the EcoR I and EcoR II, from Heamophilus influenzae and the Hind II and Hind III. These enzymes can cut DNA at specific sites can be generated in vitro ligation of the gene fragments . Researchers soon discovered endonuclease gene is composed of function and expression are very useful tools.
When the restriction endonuclease used in the seventies , when spread to many companies to start looking NEB represented within more restriction enzymes . Except for certain viruses, restriction endonuclease is found only in prokaryotes . People are looking for the new restriction endonuclease from thousands of bacteria and archaea . And prokaryotic genome sequenced data analysis showed that the restriction enzymes ubiquitous in prokaryotes – free survival of all bacteria and archaea can seem encoding restriction endonuclease .
Restriction endonuclease forms, from the size of it , they can be as small as Pvu II (157 amino acids ) can also be more than 1250 amino acids Cje I greater. In the 3000 classification purified restriction enzymes , it has been found more than 250 kinds of specific recognition sequence. Of which 30% are found in NEB . With unknown specificity of restriction endonuclease recognition sequence found work continues. People from the perspective of the analysis of biochemical study of cell extracts , but also known by computer analysis of genomic data in order to discover more . Although many of the newly discovered enzyme recognition sequence has been repeated with – that isoschizomers , there is still a new recognition sites for the enzyme being discovered .
In the 1980s , NEB began cloning and expression of restriction endonucleases . Since the cloning of the expression of the restriction endonuclease and separated from the original environment of the cell , to avoid contamination of other cells in the original enzyme , thereby enhancing the purity of the enzyme . Furthermore, to improve the cloning restriction endonuclease yields , simplifying the purification process , so that significantly reduce production costs ; easily cloned genes were sequenced , the protein is also analyzed by X -ray crystallography , which allows us to cloning product more certain .