Hamilton O. Smith

Hamilton Othanel Smith (August 23, 1931 – October 25, 2025) was an American microbiologist and a Nobel prize winner. He was jointly awarded the 1978 Nobel Prize in Physiology or Medicine. He was a leader in the field of genomics. He was born in New York City.

Hamilton Smith was, with Craig Venter, a leader in the Celera corporation's bid to analyse and sell information about the human genome. The basic idea was to find ways to make DNA sequencing cheaper so that everyone could have their DNA analysed. Then the information could be used for medical purposes.

Smith's award was for the discovery of restriction enzymes. These are enzymes that cut DNA at specific places. Such enzymes, found in bacteria and archaea, probably evolved to provide a defense mechanism against invading viruses. Inside a bacterial host, the restriction enzymes selectively cut up foreign DNA. Host DNA is modified so it does not get cut up. The host DNA is methylated by a modification enzyme (a methylase) to protect it from the restriction enzyme’s activity. Together, these two processes are called the restriction modification system. To cut the DNA, a restriction enzyme makes two cuts, once through each sugar-phosphate backbone (i.e. each strand) of the DNA double helix. 

Smith was diagnosed with lymphoma in 2016. He died on October 25, 2025 at his home in Ellicott City, Maryland at the age of 94. 

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Category:1931 births
Category:2025 deaths
Category:American Nobel Prize winners
Category:American microbiologists
Category:Nobel Prize in Physiology or Medicine winners
Category:Deaths from lymphoma
Category:Scientists from New York City
Category:Scientists from San Diego