X-Ray and Crystallographic Studies of Plant Virus Preparations. Iii

Abstract

These papers give an account of an optical and x-ray examination of preparations of plant virus substances isolated by Bawden and Pirie, in particular of those of tobacco mosaic disease. They open with a historical survey of the work, indicating the order in which new phenomena were discovered. The subsequent treatment is divided into three parts: I. Introduction and preparation of specimens. II. Modes of aggregation of virus particles. III. (1) The structure of the particles. (2) Biological implications. Part I, after an historical introduction, describes the method of preparation, from solutions of the virus, of optically oriented specimens of different concentrations. For their examination special x-ray apparatus was developed, in particular cameras working with very low angles and capable of indicating spacings up to 1000 Å. In Part III, Section 1 deals with the x-ray evidence on the internal structure of the particles. Even in solution, they have an inner regularity like that of a crystal. Virus preparations are thus in a sense doubly crystalline. Closer analysis reveals that the x-ray patterns are not directly comparable to those of a crystal as many of the reflections do not obey Bragg's law, but can be understood on the theory of gratings of limited size. The structure seems to consist of sub-units of the dimensions of approximately 11 Å cube, fitted together in a hexagonal or pseudohexagonal lattice of dimensions—a = 87 Å, c = 68 Å. Contrary to what earlier observations seemed to indicate, the particle seems to be virtually unchanged by drying and must therefore contain little water. There are marked resemblances with the structure of both crystalline and fibrous protein, but the virus structure does not belong to any of the classes hitherto studied. There are indications that the inner structure is of a simpler character than that of the molecules of crystalline proteins. Part III, Section 2 contains a comparative study of the optical and x-ray examinations of three strains of tobacco mosaic virus, two of cucumber disease virus, two of potato virus X, and the virus of bushy stunt disease of tomato. In the last case x-ray measurement confirmed the deduction from its cubic crystal habit that it was composed of spherical rather than long particles, and showed that these had a diameter when dry of 276 Å and were arranged in a body-centred cubic close packing. This single example is sufficient to show that the elongated particle form which gives rise to all the anomalous physical properties of the other viruses studied is of no essential biological importance. The similarity and differences observed between the physical properties of these preparations run closely parallel to their clinical and serological classification. Finally, the biological implications of these results are discussed together with possible applications of the new methods of examination to the study of colloid and biological problems.

Some reflective properties of the tapetum lucidum of the cat's eye

“…However, the distance between adjacent rodlets is an order of magnitude greater than that over which conventional electrostatic 'long range' forces can act, e.g. less than 150 A in liquid crystals of the tobacco mosaic virus (Bernal & Fankuchen, 1941), and even if each rodlet were surrounded by an extensive repulsive field it would be difficult to explain the observation of Schultze (1872) and Pedler (1963) that when a domain is broken open clumps of rodlets stick together. An alternative might be that each rodlet is surrounded by a shell having the same refractive index and the same appearance in electron micrographs as the matrix.…”

The Current Picture of the Structure and Assembly of Tobacco Mosaic Virus

“…Soon after its initial purification by Stanley (1935) investigations of its structure were begun using both chemical and X-ray diffraction techniques (Bawden & Pirie, 1937;Bernal & Fankuchen, 1941). Moreover, the problems in solving such a large structure led to many developments in techniques.…”

Chiral symmetry breaking by spatial confinement in tactoidal droplets of lyotropic chromonic liquid crystals

“…The N domains emerged as spindle-like "tactoids" (3,4) with the axes of rods following the meridians of the spindles. Besides TMV dispersions (2,5), the N tactoids have been experimentally documented in water dispersions of many other materials, such as vanadium pentoxide (3,4,6,7), bohemite rods (8), fd viruses (9, 10), f-actin (11), carbon nanotubes (12), as well as in lyotropic chromonic liquid crystals (LCLCs) (13,14).…”