Which American postdoctoral student joined Franklin's TMV team in 1955?

Donald Caspar joined Rosalind Franklin’s tobacco mosaic virus team as an American postdoctoral student in 1955.

Franklin moved to Birkbeck College in 1953 and built a research programme around viruses, especially tobacco mosaic virus, or TMV. Caspar joined the group to investigate the precise location of RNA within the virus particle, complementing Franklin’s X-ray crystallographic work on its structure.

Their results appeared in separate but companion papers in Nature on 10 March 1956. Together, the papers showed that TMV was a hollow rod and that its RNA ran along the inner surface beneath the protein coat. Caspar’s paper examined the virus’s radial density distribution, while Franklin’s focused on the RNA location.

Caspar later became a leading structural biologist and helped develop the Caspar–Klug theory of virus architecture with Aaron Klug. Alfred Hershey, Seymour Benzer, and Matthew Meselson were important American geneticists or molecular biologists, but they were not the postdoctoral researcher who joined Franklin’s TMV group.