"Virus structure: general principles"

Date:
[1956]
Reference:
PP/CRI/H/2/12
Catalogue details

Licence: In copyright

Credit: "Virus structure: general principles". Source: Wellcome Collection.

    2/15
    STRUCTURE AND MORPHOLOGY OF TOBACCO MOSAIC VIRUS AND RELATED SUBSTANCES Rosalind E. Franklin, K. C. Holmes and A. Klug Birkbeck College Crystallography Lab., Univ. of London Tobacco mosaic virus (TMV) protein consists of structurally equivalent or near-equivalent subunits in helical array around the long axis of the particle. Recent accurate X-ray diffraction measurements, made possible by H. Fraenkel-Conrat's prepara tion of a mercury-substituted TMV, shows that the axial repeat period of 69 A contains 49 such subunits distributed over three turns of the helix. This means that the molecular weight of the subunit must be approximately 20,000, close to the minimum molecular weight of the protein as determined by chemical methods. (It has now become clear that the suggestion, based on earlier X-ray diffraction work, that there were two chemical subunits to each structural subunit was wrong.) The surface of the TMV particle has been shown to bear a helical groove of considerable depth (probably about 30 A) following the line of the main protein helix. The location and molecular structure of the ribonucleic acid (RNA) in the intact TMV particle has been studied by measuring the differences between the X-ray diffraction diagrams of TMV and of repolymerized RNA-free TMV protein (A-protein) prepared by G. Schramm. In this way it has been shown that the phosphate backbone chains of the RNA molecules he at a radial distance of about 40 A from the axis of the particle. Thus the RNA does not form a compact axial core, but is deeply embedded in the virus protein and its molecular structure and chain direction must therefore be closely related to the structural arrangement of the protein. MATERIAL IN VIRUS PREPARATIONS NOT NECESSARY FOR THE MANIFESTATION OF CHARACTERISTIC VIRUS PROPERTIES N. W. PlRIE Rothamsted Experimental Station, Harpenden, Hertfordshire The purification of viruses is an interesting academic exercise. It tells us something about the simplest type of particle that can initiate infection in a specified host. But there is no reason to assume that material as simple as the purified preparation is responsible for the transmission of infection from cell to cell. It is as likely that something more complex is the normal vehicle and that this is reformed when a cell is infected with a purified preparation by the accretion of those cell components from which, during purification, we have laboriously separated it. Furthermore there is no reason to expect that the only consequence of infecting a cell is that copies of the infecting agent appear. There is obviously a general metabolic derange ment and a diverse group of its products may appear in partially or even rigorously purified preparations. To give the chemical and physical study of virus preparations some practical value it is essential that more information should be given about the status of the preparation that is being examined. There are two extreme types of material that may be present, although not necessary for the preparation to be infective: non-infective particles with properties similar to the infective particles may accompany them, and material may be attached to the infective particles but may be separatable from them without loss of infectivity. There are probably some equilibrium intermediate stages. Examples illustrating these phenomena will be discussed.
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