"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.

    1/15
    VIRUS STRUCTURE : GENERAL PRINCIPLES F. H. C. Crick and J. D. Watson Cavendish Laboratory, Dept. of Physics, Cambridge University The paper will deal mainly with small viruses and especially those whose structure is rather simple. It falls into two parts. In the first part we consider why these small viruses are all either rods or spheres. We can account for this by the hypothesis that the protein part of the virus is constructed from a number of identical subunits, related by symmetry elements. This follows from the general principle which we can apply whenever, on the molecular level, a structure of a definite size and shape has to be built up from smaller units, namely, that the packing arrangements are likely to be repeated again and again. The way in which this principle may apply to the RNA component of the virus will be discussed. The second part is more speculative and attempts to answer the question : Why does the virus contain subunits ? One possible explanation is as follows. If a virus must possess its own specific protein, and if synthesis of the sequence of the amino acids in a polypeptide chain is controlled by the sequence of bases in the RNA, then on any simple inter-relationship the amount of RNA inside a virus does not contain sufficient information to control the production of an extremely large protein molecule, but only one of moderate size. The virus induces its host cell to produce many copies of this molecule which then aggregate to form the protein shells of new virus particles. STRUCTURE AND SUBSTRUCTURE OF SOME VIRUSES AS REVEALED BY ELECTRON MICROSCOPY Robley C. Williams Virus Laboratory, University of California, Berkeley The electron microscope has been used extensively in the examination of the morphology of intact viruses and of their substructures. New techniques have shown that several of the viruses, when intact, have polyhedral shapes. Examination of thin sections of large, intracellular viruses has shown them to have characteristic nuclear and membrane components. Sub structures of purified viruses have been disclosed by procedures involving disintegration. We have investigated particularly the substructure of the particles of T2 bacteriophage and of tobacco mosaic virus. T2 bacteriophage can be disjointed, with retention of adsorptive activity, by freezing and thawing. The virus particles disjoin into several distinct components, easily recognizable and count able before and after exposure to host bacteria. The results confirm the notion that adsorption is tail-first. The tail is a complex structure whose component parts can be associated in detail with the mechanism of adsorption and DNA injection. Degradation of TMV by treatment with alkali and with detergents has disclosed the shape and size of the larger, stable substructures of the protein portion and has led to the localiza tion of the RNA. The stable protein portion exists as per forated discs (M.W. 50 400,000) resembling the forms taken by partially polymerized X-protein. The RNA bundle is localized within a central tube extending throughout the virus particle. Reconstitution experiments indicate the manner of repolymeriza- tion of the nucleoprotein, and show a close correlation between infectivity and the existence of virus particles longer than 3000 Â.