people distributed over the basement, first and second floors on two different staircases." RNA research Franklin continued to explore another major nucleic acid, RNA, a molecule equally central to life as DNA. She again used X-ray crystallography to study the structure of the tobacco mosaic virus (TMV), an RNA virus. Her meeting with Aaron Klug in early 1954 led to a longstanding and successful collaboration. Klug had just then earned his PhD from Trinity College, Cambridge, and joined Birkbeck in late 1953. In 1955 Franklin published her first major works on TMV in Nature, in which she described that all TMV virus particles were of the same length. This was in direct contradiction to the ideas of the eminent virologist Norman Pirie, though her observation ultimately proved correct. Franklin assigned the study of the complete structure of TMV to her PhD student Holmes. They soon discovered (published in 1956) that the covering of TMV was protein molecules arranged in helices. Her colleague Klug worked on spherical viruses with his student Finch, with Franklin coordinating and overseeing the work. As a team, from 1956 they started publishing seminal works on TMV, cucumber virus 4 and turnip yellow mosaic virus. Franklin also had a research assistant, James Watt, subsidised by the National Coal Board and was now the leader of the ARC group at Birkbeck. The Birkbeck team members continued working on RNA viruses affecting several plants, including potato, turnip, tomato and pea. In 1955 the team was joined by an American post-doctoral student Donald Caspar. He worked on the precise location of RNA molecules in TMV. In 1956 he and Franklin published individual but complementary papers in the 10 March issue of Nature, in which they showed that the RNA in TMV is wound along the inner surface of the hollow virus. Caspar was not an enthusiastic writer, and Franklin had to write the entire manuscript for him. In 1957 her research grant from ARC expired, and was given a one-year extension ending in March 1958. Expo 58, the first major international fair after World War II, was to be held in Brussels in 1958. Franklin was invited to make a five-foot high model of TMV, which she started in 1957. Her materials included table tennis balls and plastic bicycle handlebar grips. The Brussels world's fair, with an exhibit of her virus model at the International Science Pavilion, opened on 17 April, one day after she died. Polio virus In 1956, Franklin visited the University of California, Berkeley, where colleagues had suggested her group research the polio virus. In 1957 she applied for a grant from the United States Public Health Service of the National Institutes of Health, which approved £10,000 for three years, the largest fund ever received at Birkbeck. In her grant application, Franklin mentioned her new interest in animal virus research. She obtained Bernal's consent in July 1957, though serious concerns were raised after she disclosed her intentions to research live, instead of killed, polio virus at Birkbeck. Eventually, Bernal arranged for the virus to be safely stored at the London School of Hygiene and Tropical Medicine during the group's research. With her group, Franklin then commenced deciphering the structure of the polio virus while it was in a crystalline state. She attempted to mount the virus crystals in capillary tubes for X-ray studies, but was forced to end her work due to her rapidly failing health. After Franklin's death, Klug succeeded her as group leader, and he, Finch and Holmes continued researching the structure of the polio virus. They eventually succeeded in obtaining extremely detailed X-ray images