Monday's Molecule #73 is tobacco mosaic virus (TMV). As its name implies, TMV is a plant virus that infects tobacco and related species. It was one of the first viruses to be identified and one of the first to be purified.
A large number of studies have been done with TMV because it is so easy to purify and because of its simple structure. The virus is composed of 2130 copies of a small coat protein (158 amino acids) wrapped around a single-stranded RNA molecule of 6000 nucleotides. Stanley won the Nobel Prize in 1946 for crystallizing TMV—a result that was widely interpreted as evidence that proteins were the genetic material (the RNA component wasn't recognized). Watson studied TMV crystals in order to learn about helices. Later on Rosalind Franklin worked on the structure of TMA with Stanley. Aaron Klug worked out the mechanism of assembly based on the demonstration by Fraenkel-Conrat and Williams (1955) that purified coat protein and purified RNA could be mixed and spontaneously reassembled to form active virus particles [See Citation Classic from Oct. 26, 2007].
Later, Fraenkel-Conrat mixed and matched coat protein and RNA from different viruses and used the hybrids to infect plant cells. He showed that the new viruses always had the properties of the RNA and not the coat protein, demonstrating that the genetic material was the RNA and not the protein.
Early workers on in vitro translation uses TMV RNA as a template since it was one of the few examples of pure mRNA.
[Image Credits: The figures are from Alberts et al. (2002) Figure 3-33.]
Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K. and Walter, P. (2002) The Molecular Biology of the Cell 4th ed., Garland Science, New York (USA)
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