Infectious in vivo and in vitro transcripts from a full-length cDNA clone of PVY-N605, a Swiss necrotic isolate of potato virus Y

A full-length cDNA clone of the potato virus Y (PVY) genome was obtained after cloning difficulties in Escherichia coli were overcome. These difficulties were mainly due to the expression of the CI gene from upstream prokaryotic promoter-like elements within the PVY genome. To overcome this problem, PVY cDNA was maintained in two subclones which were ligated before infection. A plasmid in which these two fragments were contained could be propagated in some E. coli strains but was unstable and yielded only low levels of plasmid DNA. Replacement of the 35S promoter by the SP6 promoter slightly increased the stability of the plasmid and its RNA transcripts were infectious when capped with m7G(5')ppp(5')G. Using two inoculation methods (mechanical or biolistic) the cDNA and its RNA transcript proved infectious on three Nicotiana species and on Solanum tuberosum.

Influence of surface and protein modification on immunoglobulin G adsorption observed by scanning force microscopy

Scanning force microscopy has been used successfully to produce images of individual protein molecules. However, one of the problems with this approach has been the high mobility of the proteins caused by the interaction between the sample and the scanning tip. To stabilize the proteins we have modified the adsorption properties of immunoglobulin G on graphite and mica surfaces. We have used two approaches: first, we applied glow discharge treatment to the surface to increase the hydrophilicity, favoring adhesion of hydrophilic protein molecules; second, we used the arginine modifying reagent phenylglyoxal to increase the protein hydrophobicity and thus enhance its adherence to hydrophobic surfaces. We used scanning force microscopy to show that the glow discharge treatment favors a more homogeneous distribution and stronger adherence of the protein molecules to the graphite surface. Chemical modification of the immunoglobulin caused increased aggregation of the proteins on the surface but did not improve the adherence to graphite. On mica, clusters of modified immunoglobulins were also observed and their adsorption was reduced. These results underline the importance of the surface hydrophobicity and charge in controlling the distribution of proteins on the surface.

Preparation of isolated biomolecules for SFM observations: T4 bacteriophage as a test sample

The T4 bacteriophage has been used to investigate protocols for the preparation of samples for scanning force microscopy in air, in order to obtaining reproducible images. The resolution of images and the distribution of bacteriophages on the substrate depends on the buffer type, its concentration, the surface treatment of substrate, and the method of deposition. The best imaging conditions for the phages require dilution in a volatile buffer at low ionic strength and adsorption onto hydrophilic surfaces. When imaging with the scanning force microscopy the quality of the images is influenced by the vertical and lateral forces applied on the sample and by the tip geometry.