Inhibitor of Virus Replication from Protoplasts of a Hypersensitive Tobacco Cultivar Infected with Tobacco Mosaic Virus is Associated with a 23-K Protein Species

Abstract

A specific protein with an approximate molecular weight of 23 K was observed consistently by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) from crude preparations of an inhibitor of virus replication (IVR) released into the culture medium from protoplasts of a hypersensitive tobacco cultivar infected with tobacco mosaic virus. Electroeluted protein from SDS-PAGE gels was biologically active with about a 20-fold increase in specific activity over that of the crude preparation. The active fraction revealed only one protein band at 23 K in PAGE, providing evidence that the 23-K protein is IVR purified to a high degree. A homologous antiserum to the 23-K protein was prepared. The antiserum was highly specific for IVR and efficiently eliminated its antiviral activity. Western blots of IVR extracted from protoplasts or leaf tissue of hypersensitive tobacco cultivar revealed a single 23-K protein band.