ELECTRON-MICROSCOPIC EVIDENCE FOR THE LOCALIZATION OF RIBONUCLEIC ACID IN THE PARTICLES OF TOBACCO MOSAIC VIRUS

Abstract

Purified virus (.05% concn.) was heated for various periods at 85[degree]C in a .02% solution of Duponol C, after which the solution was cooled and diluted 30 times in water for spraying on microscopic grids. Electron-micrographs of material heat-treated for 60 seconds showed rods of the same width as untreated particles, but somewhat shorter and having fibers (30-40 A in diameter) attached centrally to the ends of the rods. Continued heat treatment resulted in disappearance of the rods and the appearance of naked fibers approximately 3000 A long. When the material was diluted in a 0.00001% solution of crystalline ribonuclease and incubated for 1 hour at 37[degree]C before spraying, the fibers almost completely disappeared, whereas crystalline trypsin had no effect. Examination of X-protein indicated a tubular structure with the central channel 30-70 A wide. If the virus protein is aggregated in the same way as X-protein the central channel could contain an RNA fiber. These lines of evidence support the theory that RNA is localized in a central core of the virus particle.