A simple method to estimate the isoelectric point of modified Tomato bushy stunt virus (TBSV) particles

We present a simple method to estimate the isoelectric point (pI) of Tomato Bushy Stunt particles. We demonstrate that the combination of agarose gels with different pH buffers can be used to electrophorese the virus particles and their migration patterns can be compared. This method allows us to estimate the pI of the virus particles (wild type, wt, and genetically modified particles) and to monitor the effect of the pI of modified peptide side chains of the viral capsid subunit on the pI of the whole virus particle.

Interaction of DNA with the movement proteins of geminiviruses revisited

Geminiviruses manage the transport of their DNA within plants with the help of three proteins, the coat protein (CP), the nuclear shuttle protein (NSP), and the movement protein (MP). The DNA-binding capabilities of CP, NSP, and MP of Abutilon mosaic virus (AbMV; family Geminiviridae; genus Begomovirus) were scrutinized using gel mobility shift assays and electron microscopy. CP and NSP revealed a sequence-independent affinity for both double-stranded and single-stranded DNA, as has been previously reported for other begomoviruses. MP interacted selectively with dimeric supercoiled plasmid DNA in the electrophoretic assay. Further apparent size- and form-selective binding capacities of MP have been previously reported for another geminivirus (Bean dwarf mosaic virus), but in the case of AbMV, they have been identified as the result of electrophoretic interference rather than of complex formation. Without these complications, electron microscopy confirmed the assembly of double-stranded supercoiled DNA with NSP and MP into conspicuous structures and provided the first direct evidence for cooperative interaction of MP, NSP, and DNA. Based on these results and previous ones, a transport model of geminiviruses is discussed in which NSP packages DNA and MP anchors this complex to the protoplasmic leaflets of plasma membranes and microsomes for cell-to-cell movement.

Turnip crinkle virus genes required for RNA replication and virus movement

We have used infectious in vitro transcripts from mutagenized turnip crinkle virus (TCV) cDNA clones to identify the gene products required for viral RNA replication, virion assembly, and intercellular movement. Previous sequence analysis of the TCV genome revealed the presence of five open reading frames which had the potential to encode gene products of 88, 38, 28, 9, and 8 kDa. Inoculation of protoplasts with infectious RNA revealed that only the p28 and p88 gene products are required for viral RNA synthesis. Although the p8 and p9 gene products were dispensable for RNA replication and virion assembly in protoplasts, mutations in the p8 and p9 genes prevented the production of systemic infections in plants. No viral RNA or protein was observed in the inoculated or systemic leaves of plants inoculated with transcripts synthesized from p8 or p9 mutant cDNAs. In contrast to these results, viral RNA was recovered from the inoculated, but not the systemic leaves, of plants inoculated with an RNA lacking the coat protein (CP) gene. With the CP mutant, no symptoms were observed on normally systemic hosts, but small local lesions were induced on Chenopodium amaranticolor. These results indicate that p8, p9, and CP are required for viral movement.

Detection of turnip crinkle virus on agarose gel electropherograms at the nanogram load level

The previous conditions for the physical characterization of turnip crinkle virus (TCV) by quantitative agarose gel electrophoresis [1, 2] were limiting the method to the microgram load level and were therefore insufficiently sensitive to satisfy the need in many areas of virology for detection of viruses containing single-stranded RNA at the nanogram level. The present report remedies that defect by presenting a technique compatible with the nanogram load level of such viruses. The technique is based on a reduction of gel thickness and on the use of silver staining.

Physical identification of a virus in a crude leaf extract by its Ferguson plot in agarose gel electrophoresis

Crude extracts of turnip crinkle virus upon agarose gel electrophoresis yield (i) virus patterns unperturbed by contaminants; (ii) plots of mobility vs. gel concentration (Ferguson plots) parallel with those of the purified virus. The parallelism suggests similarity in size and shape but a lower net charge for the crude virus. This result is obtained when gel electrophoresis is carried out either in a continuous buffer or in a discontinuous (moving boundary electrophoresis) buffer system. The latter mode has the substantial benefit of electrophoretic (auto-)concentration of dilute virus sample prior to resolution. Thus, the Ferguson plot analysis in a discontinuous buffer system of turnip crinkle virus can be viewed as a model procedure for the physical identification of other viruses contained in dilute extracts, feasible even in the absence of a prior knowledge as to the nature of, or isolation of, the virus.

Gel electrophoresis of intact subcellular particles

The review describes the application of gel electrophoresis to the characterization and separation of viruses, ribosomes, vesicles and other subcellular particles. The preparation of the sample, the choice of the buffer, the gel medium, the apparatus and the detection of the particle (staining and scanning) as well as the necessary theory are discussed. This includes the mathematical evaluation of experimental data on the basis of Ferguson plots using the extended Ogston theory. Simple methods and sophisticated computer simulation techniques are described and exemplified in application to the determination of particle size and charge, the pore size of the gel (unpublished data) and the two-dimensional agarose electrophoresis (unpublished). It is shown that the nature of the particle (e.g. spherical or rod-shaped, pliable or rigid texture) determines the shape of the non-linear Ferguson plot. In addition, the review gives a number of practical applications of gel electrophoresis, isoelectric focusing, titration curves and immuno-electrophoresis to subcellular particles. Pros and cons are evaluated. A comparison with other analytical procedures is made. The review is concluded by a futuristic outlook.

Agarose gel electrophoresis of bacteriophages and related particles

Viruses and related particles have been fractionated by electrophoresis through gels. For agarose gels, the radius at the exclusion limit for spheres varies from 1500 nm in a 0.04% gel to 3.6 nm in a 4.0% gel. Thus, the size of the gel's pores can be adjusted to sieve all known viruses. By measurement of electrophoretic mobility (mu) as a function of agarose concentration, the mu in the absence of a solid support (mu 0) can be determined for any particle. From the shape of a semilogarithmic plot of mu as a function of agarose percentage, a rod-shaped particle can be discriminated from a spherical particle. The sphere's radius can be determined from this plot with an accuracy of +/- 8%. Accuracy of +/- 1% has been more recently achieved using two-dimensional agarose gel electrophoresis. Though bacteriophages have been the primary object of study, the above techniques of agarose gel electrophoresis have also been applied to plant viruses and should be applicable to animal viruses. The mu 0 values measured for bacteriophages with and without their tail fibers suggest a mechanism of controlling attachment to a host. A related mechanism is proposed for the control of the virulence of animal viruses. Measurement of outer radius for different forms of the capsid of bacteriophage P22 reveals variability in outer radius too small to be detected by electron microscopy.