This prevents infection by effectively destroying the foreign DNA introduced by an infectious agent (such as a bacteriophage).
[3] In 1953, Jean Weigle and Giuseppe Bertani reported similar examples of host-controlled modification using different bacteriophage system.
[4] Later work by Daisy Roulland-Dussoix and Werner Arber in 1962[5] and many other subsequent workers led to the understanding that restriction was due to attack and breakdown of the modified bacteriophage's DNA by specific enzymes of the recipient bacteria.
[6] When these enzymes were isolated in the laboratory they could be used for controlled manipulation of DNA, thus providing the foundation for the development of genetic engineering.
Werner Arber, Daniel Nathans, and Hamilton Smith were awarded the Nobel Prize in Physiology or Medicine in 1978 for their work on restriction-modification.
Cleavage occurs at variable distances from the recognition sequence, so discrete bands are not easily visualized by gel electrophoresis.
Cleavage occurs at a defined position close to or within the recognition sequence, thus producing discrete fragments during gel electrophoresis.
[citation needed] Type III systems have R (res) and M (mod) proteins that form a complex of modification and cleavage.
[11] Neisseria meningitidis has multiple type II restriction endonuclease systems that are employed in natural genetic transformation.
[22][23] A major advance is the creation of artificial restriction enzymes created by linking the FokI DNA cleavage domain with an array of DNA binding proteins or zinc finger arrays, denoted now as zinc finger nucleases (ZFN).
A 5–7 bp spacer between the cleavage sites further enhances the specificity of ZFN, making them a safe and more precise tool that can be applied in humans.
[25] R-M systems are major players in the co-evolutionary interaction between mobile genetic elements (MGEs) and their hosts.
[26] Genes encoding R-M systems have been reported to move between prokaryotic genomes within MGEs such as plasmids, prophages, insertion sequences/transposons, integrative conjugative elements (ICEs) and integrons.
On the other hand, all these MGEs encode a large number of solitary R-M genes, notably MTases.
It is also possible that R-M systems frequently exploit other mechanisms such as natural transformation, vesicles, nanotubes, gene transfer agents or generalized transduction in order to move between genomes.