[Formaldehyde-induced tight binding of protein to RNA in particles of rod-like virus].

The formaldehyde-induced formation of tightly bound RNA-protein complexes of rod-like plant viruses was studied. The preparations of tobacco mosaic virus and closely related cucumber virus 4 were incubated with 1.5% formaldehyde for 20-50 hrs at 50 degrees C. Then the viral particles were disrupted, free protein was removed and viral RNA was centrifuged in the linear gradient of Cs2SO4. The RNAs from the formaldehyde-untreated viruses and RNA from the formaldehyde-treated tobacco masaic virus had the density of 1.65-1.66 g/cm3, while RNA from the formaldehyde-treated cucumber virus had the density of 1.57-1.42 g/cm3, depending on the incubation time. This is indicative of the protein binding to RNA. Treatment of the cucumber virus complex with pronase resulted in a liberation of free RNA with the density of 1.66 g/cm3; incubation for 2 min at 100 degrees C in a dissociating mixture (2% sodium dodecyl sulfate + 0.2% mercaptoethanol) did not cause the dissociation of the complex. Polyacrylamide gel electrophoresis showed that the most part of the protein molecules are bound within the complex not by covalent protein-protein cross-links.