Abstract
Characteristic high molecular weight proteins have been isolated by ultracentrifugation from the juices of plants diseased with several of the less stable viruses. 1 Various lines of evidence indicate that virus activity is a property of these high molecular weight proteins. The viruses thus far studied are easily transmitted by mechanical means. Certain viruses, however, require specific insect vectors and are difficult to transmit by ordinary mechanical methods. We have made an ultracentrifugal examination of infectious juice containing such a virus, choosing for the purpose pea mosaic (pea virus 1). 2 In nature the pea and potato aphids 2 carry this disease but under favorable conditions it may be transmitted mechanically to about 75% of inoculated plants.
When the juice from infected broad bean plants, Vicia faba L., was ultracentrifuged 3 in a field of 40,000 g. for one and a half hours, appreciable amounts of a heavy material were obtained. The pellets were 2 or 3 times the size of those found in the case of the latent mosaic virus. After 3 ultracentrifugations, a solution of the pellets in water gave the usual qualitative tests for protein and the kind of absorption diagram in the analytical ultracentrifuge that is typical of purified heavy proteins. Nearly all the light “unsedimentable” proteins had been eliminated, and there were present sharp boundaries characterized by the sedimentation constants S20 = 76 × 10-13 cm. sec-1 dynes-1 and S20 = 112 × 10-13. Certain samples, in which there seemed to be some decomposition, gave a third boundary with S20 = 54 × 10-13.
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