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]
== Restriction enzymes catalog==The list includes some of the most studied examples of restriction endoncleases. The following information is given:
| as in this not listed enzyme: | EcoR70I |
The whole list contains more than 1,200 enzymes, but databases register about 4,000. [8] To make a list that is accessible to navigation, this list has been divided into different pages. Each page contains somewhere between 120-150 entries. Choose a letter to go to a specific part of the list:
Restriction Enzyme Database.
Databases and lists of restriction enzymes:
Databases of proteins:
Swiss-Prot is a curated protein sequence database which strives to provide a high level of annotation (such as the description of the function of a protein, its domains structure, post-translational modifications, variants, etc.), a minimal level of redundancy and high level of integration with other databases. TrEMBL is a computer-annotated supplement of Swiss-Prot that contains all the translations of EMBL nucleotide sequence entries not yet integrated in Swiss-Prot.
A restriction enzyme, restriction endonuclease, REase, ENase orrestrictase is an enzyme that cleaves DNA into fragments at or near specific recognition sites within molecules known as restriction sites. Restriction enzymes are one class of the broader endonuclease group of enzymes. Restriction enzymes are commonly classified into five types, which differ in their structure and whether they cut their DNA substrate at their recognition site, or if the recognition and cleavage sites are separate from one another. To cut DNA, all restriction enzymes make two incisions, once through each sugar-phosphate backbone of the DNA double helix.
NlaIII is a type II restriction enzyme isolated from Neisseria lactamica. As part of the restriction modification system, NlaIII is able to prevent foreign DNA from integrating into the host genome by cutting double stranded DNA into fragments at specific sequences. This results in further degradation of the fragmented foreign DNA and prevents it from infecting the host genome.
EcoRV is a type II restriction endonuclease isolated from certain strains of Escherichia coli. It has the alternative name Eco32I.
The homing endonucleases are a collection of endonucleases encoded either as freestanding genes within introns, as fusions with host proteins, or as self-splicing inteins. They catalyze the hydrolysis of genomic DNA within the cells that synthesize them, but do so at very few, or even singular, locations. Repair of the hydrolyzed DNA by the host cell frequently results in the gene encoding the homing endonuclease having been copied into the cleavage site, hence the term 'homing' to describe the movement of these genes. Homing endonucleases can thereby transmit their genes horizontally within a host population, increasing their allele frequency at greater than Mendelian rates.
Meganucleases are endodeoxyribonucleases characterized by a large recognition site ; as a result this site generally occurs only once in any given genome. For example, the 18-base pair sequence recognized by the I-SceI meganuclease would on average require a genome twenty times the size of the human genome to be found once by chance. Meganucleases are therefore considered to be the most specific naturally occurring restriction enzymes.
In molecular biology, REBASE is a database of information about restriction enzymes and DNA methyltransferases. REBASE contains an extensive set of references, sites of recognition and cleavage, sequences and structures. It also contains information on the commercial availability of each enzyme. REBASE is one of the longest running biological databases having its roots in a collection of restriction enzymes maintained by Richard J. Roberts since before 1980. Since that time there have been regular descriptions of the resource in the journal Nucleic Acids Research.
