APRIL 2000
Pioneers of Discovery
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Molecular Biology's
Cutting Edge
By Melissa Hendricks

Restriction enzymes are an indispensable tool for molecular biologists. Like biochemical scissors, they cut at predictable sites in the letters of DNA's chemical sequence, and have enabled researchers to decipher the construction and function of genes. In the 30 years since Hopkins scientists Hamilton Smith and Daniel Nathans discovered them, researchers have used them to clone genes, map and sequence most of the human genome, and launch the biotechnology industry. At Hopkins alone, they've been used in hundreds of labs.

In 1978, Smith, Nathans, and Swiss microbiologist Werner Arber were awarded the Nobel Prize in physiology or medicine for their work on site-specific restriction enzymes. Arber had hypothesized their existence. Smith (MD '56) then discovered the first site-specific restriction enzyme in the late 1960s, and Nathans used restriction enzymes to cut the DNA of a tumor virus called SV40 into distinct pieces. Nathans used those fragments to map the genes of SV40 and identify the genes the virus used to command tumor growth. Smith is now a senior scientist at Celera Genomics, in Rockville, Md. Nathans was University Professor of Molecular Biology and Genetics until his death this past November.

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