Survey and Characterization of Viruses in Sweetpotato from Zimbabwe.

Thirty-one clones of sweetpotatoes collected from some parts of Zimbabwe were used as inoculum sources to mechanically inoculate 13 experimental hosts: Chenopodium amaranticolor, C. quinoa, Cucumis sativus, Datura stramoniumitalic, Gomphrena globosa, Ipomoea purpurea, I. quamoclit, I. rubrocorulea, Nicotiana benthamiana, N. clevelandii, N. glutinosa, N. rustica, and N. tabacum. Systemic vein clearing was observed in N. benthamiana inoculated with buffered sap from nine clones. Purification of the vein clearing inducing agent from one of the sweetpotato clones gave yields ranging from 2 to 17 mg/kg and the A260nm/A280nm was around 1.2. Electron microscopy revealed flexuous filamentous particles with a modal length of 830 nm. Protein analysis of purified virus preparations by sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed a major protein band of 40 kDa, and this was assumed to be the viral coat protein. Minor protein bands of 27, 37, and 46 kDa were also observed. The viral protein degraded upon storage at 4°C over time to yield a protein band of 27 kDa. Polyclonal antiserum was produced against the purified virus. Protein A gold labeling of the purified virus incubated with available antisera; sweetpotato chlorotic stunt virus (SPCSV), sweetpotato feathery mottle virus strain russet crack (SPFMV-RC), sweetpotato feathery mottle virus, sweetpotato mild mottle virus, sweetpotato latent virus, sweetpotato chlorotic fleck virus, and sweetpotato caulimo-like virus resulted in a higher labeling density with the antiserum of SPFMV-RC than with the antiserum of SPCSV, while the other sera did not react. Further characterization of the vein clearing inducing agent was attempted by reverse transcription-polymerase chain reaction amplification of total RNA with degenerate primers for potyviruses and an oligo dT primer and PCR products of correct size were obtained. The nucleotide sequence was determined and the amino acid of the polyprotein deduced. Comparison with other strains of SPFMV showed strong similarity except for an insertion of 22 amino acids at the N-terminus of the coat protein. The coat protein size of 335 amino acids is the biggest SPFMV so far determined.

Monodisperse polymer-virus hybrid nanoparticles.

Self-assembly of polystyrene sulfonate and modified cowpea chlorotic mottle virus protein yields monodisperse icosahedral nanoparticles of 16 nm size.

A virus-based single-enzyme nanoreactor.

Most enzyme studies are carried out in bulk aqueous solution, at the so-called ensemble level, but more recently studies have appeared in which enzyme activity is measured at the level of a single molecule, revealing previously unseen properties. To this end, enzymes have been chemically or physically anchored to a surface, which is often disadvantageous because it may lead to denaturation. In a natural environment, enzymes are present in a confined reaction space, which inspired us to develop a generic method to carry out single-enzyme experiments in the restricted spatial environment of a virus capsid. We report here the incorporation of individual horseradish peroxidase enzymes in the inner cavity of a virus, and describe single-molecule studies on their enzymatic behaviour. These show that the virus capsid is permeable for substrate and product and that this permeability can be altered by changing pH.