A restriction enzyme (or restriction endonuclease) is an enzyme that cuts DNA at specific recognition nucleotide sequences known as restriction sites. Restriction enzymes are commonly classified into three 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 (i.e. each strand) of the DNA double helix. These enzymes are found in bacteria and archaea and probably evolved to provide a defense mechanism against invading viruses.Inside a bacteria, the restriction enzymes selectively cut up foreign DNA in a process called restriction; while host DNA is protected by a modification enzyme (a methylase) that modifies the bacterial DNA and blocks cleavage. Together, these two processes form the restriction modification system.
Created: 2019-07-04 09:37:20 CDT (-0500)
Last modified: 2019-07-04 09:37:20 CDT (-0500)