David Baltimore

'Giant discoveries' in molecular biology won him a Nobel prize and a stellar reputation among US scientists

- Patrick Kidd

When David Baltimore received the Nobel prize for physiology or medicine in 1975, he said that a virologist was among the luckiest of scientists. “He can see into his chosen pet down to the details of all its molecules.” Ever since high school, he had been fascinated by the tiniest building blocks of life, where giant discoveries can be made.

In 1970, while studying leukaemia in mice, Baltimore discovered an enzyme that challenged the common understanding of how genetic information is transmitted. Previously, it was thought that proteins were produced in living cells by molecules known as RNA that contained a copy of DNA. However, some viruses, later known as retroviruses, worked in the opposite direction, corrupting the DNA in a host cell. Baltimore found that this was created by an enzyme called a transcriptase. His discovery allowed scientists to insert healthy genes into DNA, leading to breakthroughs in the treatment of cancer and HIV. In 1975 it earned him the Nobel prize with Renato Dulbecco and Howard Martin.

"In a single stroke, David demonstrated something that had been considered to be impossible for more than 20 years," said Carlos Lois, a colleague at Caltech (the California Institute of Technology), where Baltimore was later president. Thomas Palfrey, an economics fellow there, said: "He was one of these people who put his foot on the accelerator and never let up his whole life."