On October 25, 2025, Hamilton O. Smith, an American molecular biologist who discovered a DNA-cutting enzyme, died at the age of 94. Although the J. Craig Venture Institute and Nature published his obituary shortly after his passing, his death did not gain attention until The New York Times reported it on December 5.
Smith was born in New York City in 1931 and grew up in Urbana-Champaign, Illinois, as stated by Wikipedia. According to The New York Times, his curiosity about science ignited during his teenage years, when Smith and his brother Bunnie turned the family’s basement into a science “laboratory” with the money they earned from newspaper deliveries. He received a BA in mathematics from the University of California, Berkeley in 1952 and a medical degree from the Johns Hopkins School of Medicine in 1956, as stated by Britannica. After serving in the US Navy, Smith finished his medical residency at Henry Ford Hospital in Detroit.
During his lifetime, Smith’s most celebrated scientific achievement was the co-discovery of the first type II restriction enzyme, for which he was awarded the Nobel Prize in Physiology and Medicine in 1978 alongside two other scientists.
Type II restriction enzymes are proteins that recognize short, specific DNA sequences, usually four to eight bases long, and cut the DNA precisely at or near those sites, according to Creative Enzymes. These enzymes are part of the natural defense system bacteria and archaea use to combat viral infections. As the National Library of Medicine explains, they are indispensable tools “for characterizing genomes, sequencing genes, and assembling DNA into novel genetic arrangements.” This discovery is arguably one of the most important in molecular biology because the enzyme’s ability to cut DNA at exact, predictable sites made controlled genetic manipulation, and thus modern biotechnology, possible.
One of the earliest and most transformative applications of Smith’s discovery was the development of insulin, the hormone in our body that regulates blood sugar and is a key medicine for diabetes, according to The New York Times. Until the 1970s, diabetic patients relied on insulin from pigs and cows because it was not possible to synthesize human insulin outside the human body, according to the National Library of Medicine. This method was not ideal for humans and mass production was impossible.Using the discovered enzymes, scientists cut the DNA of E. coli, a common, harmless bacterium, into precise fragments and inserted human DNA segments containing the instructions for making insulin, which had been cut with the same enzyme. The resulting recombinant DNA was then placed back into E. coli, effectively programming the bacteria to produce human insulin. Because E. coli reproduces rapidly, this method enables large-scale production of insulin that is molecularly identical to the human hormone. Synthetic insulin created through this technique has since saved millions of lives worldwide.
Since Smith’s initial discovery, the catalog of known type II restriction enzymes has expanded to more than 3,500. They are widely used in areas such as gene cloning, forensic science, and genomics. The New York Times describes the type II enzyme as “laboratory workhorses, capable of cutting DNA’s spiraling double helix at multiple target sites.”
Beyond discovery of the restriction enzyme, Smith made several other achievements. In 1995, his team at the J. Craig Venter Institute, formerly known as the Institute for Genomic Research, completed the DNA sequencing of the genome of a bacterium, Haemophilus influenzae, which is the first complete genome sequence of any free-living organism, according to Wikipedia. In 2010, his team created the first cell made from a synthetic genome, according to Nature.
Smith’s discoveries not only changed the field of molecular biology but also made possible many medical advances that have saved millions of lives, including the creation of synthetic insulin and many of today’s genetic tools. Yet the fact that his death became widely known only after The New York Times published an article on it shows how often people like him, scientists whose quiet work makes a huge difference, fail to get the recognition they deserve. Smith’s legacy reminds us that those who help move science forward and improve human health should be appreciated far more, both during their lives and after they pass.
