Restriction Enzymes (DNA Scissors)
In 1970 Hamilton Smith isolated an enzyme that cuts DNA at one exact sequence; such restriction enzymes became the molecular scissors of genetic engineering.
Open in the interactive tree →In the early 1950s Luria, Weigle and Bertani saw that bacteriophages grow poorly in unfamiliar bacterial strains, and in the 1960s Werner Arber and Matthew Meselson traced this to enzymes that cut foreign DNA. In 1970 Hamilton Smith's group isolated HindII, which cuts at a fixed sequence, and in 1971 Daniel Nathans used such enzymes to cut a virus's DNA into reproducible pieces that could be mapped. In 1972-73 enzymes that leave 'sticky ends' let Paul Berg's group, then Cohen and Boyer, join DNA from different sources. Arber, Smith and Nathans shared the 1978 Nobel Prize in Physiology or Medicine.
Prerequisites
- Viruses Discovered1892-1898Bacterial defence against bacteriophage viruses revealed the enzymes.
- Structure of DNA1953Each enzyme recognises and cuts one specific sequence of DNA letters.
Unlocks
- Genetic Engineering1973Cohen and Boyer's 1973 experiment cut and joined DNA with restriction enzymes.
- DNA Fingerprinting1984DNA is cut by restriction enzymes into fragments whose lengths differ between people.