Smith, Hamilton Othanel (1931– )

US microbiologist who was awarded a Nobel Prize for Physiology or Medicine in 1978 with his colleague Daniel Nathans for their discovery of restriction enzymes and their application to molecular genetics. Restriction enzymes are enzymes that can cleave genes into fragments.

Smith was born in New York and studied at the University of California, Berkeley, and at Johns Hopkins University. In 1964 he returned to Johns Hopkins, becoming professor in 1973.

Werner Arber, a Swiss microbiologist, discovered restriction enzymes in the 1960s. Smith, working independently of Arber, verified Arber's findings and was also able to identify the gene fragments. Smith collaborated with Nathans on some of this work.

As a result of the work of Nathans, Smith, and Arber (who also shared the Nobel Prize), it is now possible to determine the chemical formulas of the genes in animal viruses, to map these genes, and to study the organization and expression of genes in higher animals.