Tomato bushy stunt virus, study

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. 

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. 

Calcium binding to tomato bushy stunt virus has been studied using the synchrotron Laue method (Hajdu et al 1989). The non-crystallo-graphic symmetry of the virus crystal aided the clarity of the final map in showing up the calcium sites. A novel spatial deconvolution algorithm was used to obtain intensity estimates of the individual diffraction spots (Shrive, Clifton, Hajdu and Greenhough 1990). 

In collaboration with the Virology Laboratory of the Institut de Biologie Moleculaire et Cellulaire in Strasbourg, the Laboratory of Molecular Acoustics has studied the ultrasonic absorption of two small icosahedral viruses, bromegrass mosaic virus (BMV) and tomato bushy stunt virus (TBSV). Measurements carried out between 0.6 and 40 MHz showed that ultrasonic waves in the MHz range are absorbed much more by capsids than by dissociated protein. Examples of ultrasonic spectra of solutions of BMV protein capsids and of subunit-dimers are shown in Fig. 1 (at 5 mg/ml in 10 mM Na cacodylate, 1.00 M NaCl, at 23°C capsids , pH=4.80 dimers o, pH = 6.6o). Spectra obtained for BMV (A, pH = 5 00, at the same particle concentration as for the BMV capsids, otherwise similar conditions) and for the pure solvent ( — ) are also shown. 

This last is no mean accomplishment, for despite years of thorough physicochemical studies of plant viruses by American workers, Bawden and Pirie (26) still maintain that tomato bushy stunt virus is the only plant virus intensively studied for which there is no evidence of variability in the end products. The discussion has hardly been less acrimonious for the animal viruses. Most recently, Beard (28) has taken up the hypothesis that a single fully active elementary body (virus particle) may act to induce a lesion in an ideally susceptible host, a subject previously given extended concentration by Lauffer and Price (184). This question may only be clarified when more information is available about Dulbecco s preliminary finding that single animal virus particles can cause plaques on solid tissue culture. 

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. 

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