Tobacco bushy stunt virus

A nucleic acid can never code for a single protein molecule that is big enough to enclose and protect it. Therefore, the protein shell of viruses is built up from many copies of one or a few polypeptide chains. The simplest viruses have just one type of capsid polypeptide chain, which forms either a rod-shaped or a roughly spherical shell around the nucleic acid. The simplest such viruses whose three-dimensional structures are known are plant and insect viruses the rod-shaped tobacco mosaic virus, the spherical satellite tobacco necrosis virus, tomato bushy stunt virus, southern bean mosaic vims. 

The size of this viral particle is of course larger than that of a virus with only 60 subunits. The diameter of tomato bushy stunt virus is 330 A compared with 180 A for satellite tobacco necrosis virus. The increase in volume of the capsid means that a roughly four times larger RNA molecule can be accommodated. 

One of the most striking results that has emerged from the high-resolution crystallographic studies of these icosahedral viruses is that their coat proteins have the same basic core structure, that of a jelly roll barrel, which was discussed in Chapter 5. This is true of plant, insect, and mammalian viruses. In the case of the picornaviruses, VPl, VP2, and VP3 all have the same jelly roll structure as the subunits of satellite tobacco necrosis virus, tomato bushy stunt virus, and the other T = 3 plant viruses. Not every spherical virus has subunit structures of the jelly roll type. As we will see, the subunits of the RNA bacteriophage, MS2, and those of alphavirus cores have quite different structures, although they do form regular icosahedral shells. 

Human immunodeficiency virus (HIV) type 1 p24 protein Tomato bushy stunt virus in tobacco leaf No immunogenicity assays performed. 97, 98... 

Viral coat proteins, see Southern bean mosaic virus, Tobacco mosaic virus, or Tomato bushy stunt virus... 

Redox Fe-S proteins High-potential iron protein Ferredoxin Viral coat proteins f Tomato bushy stunt virus protein I Southern bean mosaic virus protein Tobacco mosaic virus protein... 

Most of the EF-hand motifs have one water (—X). On the other hand, in Rhizopus chinensis aspartic proteinase (Suguna et al., 1987) there is one main-chain carbonyl oxygen bound to calcium and six water molecules to complete the pentagonal bipyramidal coordination. Calcium coordination has been measured in several viruses, such as Southern bean mosaic virus (Silva and Rossmann, 1985), satellite tobacco necrosis virus (Jones and Liljas, 1984), and tomato bushy stunt virus IV (Olson et al., 1983). 

Some colloids consist of well-defined molecules, with constant molecular weight and definite molecular shape, permitting them to be piled in a crystalline array. Crystalline proteins include egg albumin (MW 43000) and hemoglobin (MW 68000). Even viruses, such as, tobacco-mosaic virus, have been crystallized their molecular weights are in the neighborhood of 10,000,000 (bushy-stunt virus) to 2,000,-000,000 (vaccinia virus). 

Formation of viruses (tomato bushy stunt virus, tobacco mosaic virus)... 

Several plant viruses have been studied using X-ray crystallography and conventional X-ray sources. These are, in no particular order, TBSV (tomato bushy stunt virus), SBMV (southern bean mosaic virus) and STN V (satellite tobacco necrosis virus) - all spherical viruses - and TMV (tobacco mosaic virus) - a cylindrical virus. These virus crystals diffract relatively well and are reasonably stable to radiation. 

J. D. Bernal and I. Fankuchen, Nature, 139 (1937) 923. See further recent reviews I. Fan-KUCHEN, X- Ray Diffraction and Protein Structure, in Advances in Protein Chemistry, edited by M. L. Anson and J. T. Edsall, Vol, II, 1945, Academic Press Inc. New York and N. W. Pirie, Physical and Chemical Properties of Tomato Bushy Stunt Virus and the Strains of Tobacco Mosaic Virus in Advances in Enzymology, edited by F. F. Nord and C. H. Werkman, Vol. V, 1945, Interscience Publishers New York. See also Volume I of Colloid Science for long range forces. 

II A radically different type of nucleoprotein is that provided by the smaller RNA viruses of the elongated spiral type like tobacco mosaic, or of the polyhedral type such as tomato bushy stunt, tipula virus or poliomyelitis virus. The only one of these adequately studied has been tobacco mosaic virus, Franklin [19, 20], and here it appears that the protein and not the nucleic acid determines the structure. There is only one RNA chain and this is wound helically so that one protein is in contact with three successive nucleotides. 

A large number of icosahedral RNA viruses of diameter 28-30 nm (Fig. 7-14) attack plants, causing diseases such as tomato bushy stunt,504 southern bean mosaic,505 or turnip yellow mosaic. Best known of the helical RNA viruses is the tobacco mosaic virus (Figs. 5-41,7-8).506 507a Its genome contains 6395 nucleotides as linear ssRNA. Many strains are known. Related viruses cause cucumber green mottle508 and other plant diseases. 

As Schachman has correctly pointed out (272), the results of this test may be illusory if it is applied to a highly asymmetric particle such as tobacco mosaic virus. However, for spherical particles the test is theoretically justified and has proved practically correct in the case of bushy stunt vims. Because of the low asymmetry of... 

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