Purification and characterization of turnip mosaic virus helper component protein

ABSTRACT The helper component (HC) protein of turnip mosaic virus (TuMV) was concentrated by differential centrifugation followed by ammonium sulfate precipitation. The partially purified HC was then loaded onto a Ni(2+)-resin column that bound the HC; a histidine tag was not required for binding. The HC eluted from the column migrated as a band of about 50 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In its native state, the HC did not pass through an ultrafiltration membrane with a molecular mass cutoff of 100 kDa, which suggested that the HC is in a multimeric form when it is biologically active. The molecular mass of the multimeric form was determined by gel filtration to be approximately 145 kDa. Purified HC retained its activity for several months at -20 degrees C. Using a protein blotting-overlay protocol, purified HC interacted in vitro with an aphid-transmissible TuMV isolate, but not with a non-aphid-transmissible isolate.     

Stylet-borne virus: active probing by aphids not required for acquisition

Anesthetized aphids, whose stylets had been dipped into capillaries containing purified concentrated cucumber mosaic virus, acquired the virus and, after recovery from the anesthetic, were able to transmit it in a low percentage of cases. Although this study does not eliminate active probing as a means of virus acquisition, experimentally, it clearly establishes passive contamination of aphid mouthparts as a method of virus acquisition.     

Local Control of Microdomain Orientation in Diblock Copolymer Thin Films with Electric Fields

Local control of the domain orientation in diblock copolymer thin films can be obtained by the application of electric fields on micrometer-length scales. Thin films of an asymmetric polystyrene-polymethylmethacrylate diblock copolymer, with cylindrical polymethylmethacrylate microdomains, were spin-coated onto substrates previously patterned with planar electrodes. The substrates, 100-nanometer-thick silicon nitride membranes, allow direct observation of the electrodes and the copolymer domain structure by transmission electron microscopy. The cylinders aligned parallel to the electric field lines for fields exceeding 30 kilovolts per centimeter, after annealing at 250°C in an inert atmosphere for 24 hours. This technique could find application in nanostructure fabrication.     

Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.