An electron microscopical examination of configurations of ribonucleic acid and other polyelectrolytes

The Hall mica-replica method was used to prepare individual macromolecules for electron microscopial examination. Electron micrographs of tobacco mosaic virus RNA show irregularly contoured rod-shaped particles from volatile salt solutions. A weight average length of 1173 Å was obtained in 0.3 M ammonium acetate at 23°; particles were about 30 Å wide. In water or hot salt solutions RNA particles appear as individual globules or as clumps of globules. Long narrow strands up to 50 000 Å long and about 10 Å wide were occasionally seen in both salt and water solutions. Other weakly ionized polyelectrolytes [poly-(acrylic acid), poly-(methacrylic acid), carboxymethyl cellulose] were also viewed as globules both in salt and water solutions. A strongly ionized poly-electrolyte [poly-(vinylsulfonic acid)] appeared only as strands under a variety of conditions. The results are in agreement with a reversible “helix” ↔ coil transformation for RNA. It is suggested that weakly ionized polyelectrolytes without appreciable secondary structure coil up upon themselves during the drying process necessary for the electron microscopical preparation. Occasional long strands are explained as the result of adherence of extended fibers to the substrate by debris or polystyrene latex spheres.