The molecular weight of yeast P1 double-stranded RNA.

The molecular weight of the double-stranded RNA (Pl dsRNA) always associated with the virus-like particles that occur in the yeast Saccharomyces cerevisiae was determined to be 3.5 + 0.1 X lo6 by equilibrium sedimentation. Methylmercuric-agarose gel electrophoresis yielded a value of 1.67 + 0.11 x lo6 for the single-stranded form. The sedimentation coefficient, 0 SZO+,, was determined by boundary sedimentation to be 15.6 + 0.13 S. As part of the equilibrium sedimentation work, the effective density gradient for dsRNA in Cs2S04 was determined. By electron microscopy, the length of the dsRNA relative to the replicative form of the DNA phage G4 was found to be 0.70 & 0.01. This represents the first determination of the contour length of a dsRNA molecule of known molecular weight relative to a dsDNA molecule. Such a relative contour length, when compared with our molecular weight data, implies a relative base pair separation along the helix (dsRNA/dsDNA) of 0.79 under our spreading conditions. This value may be used in future determinations of the molecular weight of an unknown dsRNA molecule from a co-spread DNA standard if similar spreading conditions are used. The relative length measurement and the molecular weight values were used in assessing the configurations of the dsRNA and dsDNA molecules. These suggest that the RNA is in an A-like configuration and the DNA is in a B-like configuration, or that both differ proportionately from their respective fiber structures.