On this day in 1970, molecular biologist Hamilton Smith broke new ground for biotechnology. In two papers published in the Journal of Molecular Biology, he described a new class of enzymes--restriction enzymes--that scientists now use to precisely snip DNA. While studying the bacterium Haemophilus influenzae, Smith discovered that it slices up DNA from invading viruses. The blade, he found, is an enzyme that always cuts the viral DNA code where it finds a particular short sequence of nucleotides.
Smith and others later discovered many other restriction enzymes, all with their own preferred chopping sites. This specificity has made the enzymes a handy lab tool. They enable molecular biologists and geneticists to selectively chop DNA into pieces, which can then be assembled into new versions of the gene, inserted into the genomes of other organisms, or sequenced as part of an effort to map an organism's genetic material. For this work, Smith, along with Werner Able and Daniel Nathans, shared the 1978 Nobel Prize in physiology or medicine.
[Sources: Emily McMurray, Ed., Notable Twentieth Century Scientists (Gale Research Inc., ITP, 1995) and J. Mol. Biol. 51, 379-409 (1970).]