In 1951, Franklin joined a team of biophysicists led by John Randall at King’s College who were using X-ray crystallography to study DNA. The molecule had been discovered in 1869, but its structure and function weren’t yet understood. After learning X-ray crystallography at a government-run lab in France, she was already an expert in the scientific technique, which involves beaming X-rays at crystalline structures and taking photographs of the patterns created by atoms in the structures diffracting the X-rays. By measuring the sizes, angles and intensities of the patterns, researchers can create a 3-D picture of the crystalline structure.
From the beginning, Franklin famously clashed with Wilkins, who was Randall's deputy, and the two began working largely separately from one another. Wilkins had previously identified two forms of DNA appearing in the X-ray images; Franklin discovered that by adjusting the level of humidity in the specimen chamber, she could convert the crystalline, relatively dry “A” form of DNA into the wetter, paracrystalline “B” form. She shared these key insights into DNA at a seminar in November 1951, which Watson attended.
“Her notes for that lecture are very detailed,” Comfort says, adding that Franklin initially assumed both the A and B forms had a helical structure. “She describes DNA as a big helix, describes the two forms and lays out their differences…and [explains] how the structure switches from A to B depending on the relative humidity in the sample chamber.”
Franklin’s ‘Photograph 51’
Despite capturing clear evidence of the B form’s double helical structure—most notably in what became known as Photograph 51, taken in May 1952—Franklin chose to focus on the drier A form of DNA, which produced a much sharper, more detailed image than the B form. This focus pointed her away from the idea of a helix, because the A form did not appear to be helical.
“For a chemist and an X-ray crystallographer, she was doing the [form] that made the most sense,” Comfort says. “She wasn't a biologist, and so she didn't appreciate that in a living cell, the more hydrated B form was going to be much more present, because a cell is a very wet place.”
In February 1953, Wilkins showed Photograph 51 of the B form of DNA to his friend Watson at Cambridge, who along with Crick was attempting to determine the molecule’s structure mainly through building and analyzing physical models. Wilkins received the image from Raymond Gosling, who worked for both Wilkins and Franklin and had taken the photo with Franklin.
Watson later claimed that seeing Photograph 51 immediately convinced him that a DNA helix must exist. “The instant I saw the picture my mouth fell open and my pulse began to race,” he wrote in The Double Helix. Soon after that, Crick’s supervisor passed along a report on Franklin’s unpublished results, which he had received during a visit to the King’s College lab in December 1952. By late February 1953, Watson and Crick had constructed their model of the DNA double helix, which they formally announced in a landmark paper in Nature that April.
To Comfort, Watson’s version of events doesn’t ring entirely true when it comes to Photograph 51 and its importance. “Watson talks [in The Double Helix] about realizing only then that there was an A and a B form…but Franklin talked about that at the end of 1951, and she and Wilkins talked about it openly,” Comfort says. “I think he was writing it as though the photograph was the magic key because it made a good discovery narrative that allowed him to boil down and communicate an enormously complex, highly technical kind of science.”
Franklin’s Understanding of DNA’s Structure
Comfort also discounts the idea that Franklin, an expert crystallographer, did not understand the significance of the X-ray diffraction image she and Gosling had taken of DNA’s B form 10 months earlier. “She was way too good for that,” he says.
In fact, Franklin was simply more focused on the A form of DNA at the time, and was also in the process of leaving King’s College behind for a new job at Birkbeck College, also in London. Before she left, however, Franklin started a new laboratory notebook, with notes on the B form of DNA.
By late February 1953, Franklin’s notes reveal that she had not only accepted that DNA had a helical structure, probably with two strands; she had also recognized that the component nucleotides, or bases, on each strand were related in a way that made the strands complementary, allowing the molecule to easily replicate. “Franklin’s colleague Aaron Klug analyzed her research notes and said that Franklin was ‘two steps away’ from the double helix,” Comfort says. “Given a couple more months, she surely would have had it.”
Both Wilkins and Franklin (with Gosling) published separate papers in the same April 1953 issue of Nature, largely supporting Watson and Crick’s model of DNA’s structure. The earliest presentation of the double helix that June was signed by authors of all three papers, suggesting—as Comfort and Cobb point out in their article—that the discovery of DNA was seen at the time as a joint effort, not just the triumph of Watson and Crick.
Taking Full Measure of Franklin’s Contributions
Over the next five years, Franklin led a team of researchers studying ribonucleic acid, or RNA, in viruses such as polio and the tobacco mosaic virus (TMV). Diagnosed with ovarian cancer in 1956, Franklin continued her work until days before her death in April 1958. Franklin also remained in regular contact with Watson and Crick after she left King’s College, even becoming good friends with Crick and his wife, Odile.
Franklin’s unjust exclusion from the Nobel Prize, combined with Watson’s decidedly sexist portrayal in The Double Helix led many to see her as a victim of chauvinism and betrayal. A more complicated view of events reveals a scientist who was an equal contributor to the discovery of DNA’s structure, as well as a trailblazer in the all-important field of virology.
“Franklin had an incredible series of insights into how the RNA is packed within the protein shell of TMV,” Comfort says. “She was widely recognized and seen as being at the top of her field.”
