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Timelines: 1968

Prev : Next Restriction enzymes

Tools for manipulating DNA
In early 1962, professor Werner Arber and graduate student Daisy Dussoix of the University of Geneva offered a theoretical explanation for the phenomenon of genetic restriction observed in studies of bacteriophage, a virus that infects bacteria. Some bacterial strains resisted the virus – they restricted the replication of viral DNA. Scientists speculate that restriction evolved in bacteria as a natural defense against viral invaders. Arber and Dussoix proposed the presence of endonucleases, bacterial enzymes that identify, cut, and deactivate viral DNA. The idea triggered a broad search for the hypothesized molecules. In 1968, Arber and postdoc Stu Linn demonstrated the action of a restriction enzyme in E. coli B. Soon after, Harvard Professor Matthew Meselson and postdoc Robert Yuan performed the first isolation and purification of a restrictor, an enzyme from E. coli K. Restriction enzyme snip DNA molecules into pieces. In 1970, Hamilton O. Smith of Johns Hopkins University identified a restriction enzyme that cuts DNA at specific a recognition site, a specific DNA sequence. Smith's colleague, Dan Nathans showed how such molecules could be used to construct genetic and genomic restriction maps. Molecular biologists have since identified hundreds of restriction enzymes that perform highly specialized tasks in the cellular machinery. These discoveries have had massive impacts on biological research and the development of biotechnologies. With restriction enzymes, scientists can identify and ‘cut and paste’ specific nucleic acid fragments. Arber, Nathans, and Smith were awarded Nobel Prizes for their work in 1978.
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