The stiffness of dsRNA: hydrodynamic studies on fluorescence-labelled RNA segments of bovine rotavirus.

The sedimentation coefficients of dsRNA segments of bovine rotavirus were determined in the analytical ultracentrifuge. The eleven segments were separated by preparative gel electrophoresis, and isolated by elution from gel pieces. The RNA was labelled by the intercalating fluorescent dye ethidium bromide at a ratio bound dye per base pair between 0.003 to 0.018. The analytical ultracentrifuge was equipped with a fluorescence recording optics. Sedimentation coefficients could be determined with amounts of RNA as little as 8 ng. All sedimentation coefficients were extrapolated to zero-concentration, zero-dye binding, and zero-impurities from the preparative gel electrophoresis. The hydrodynamic model of flexible cylinders was applied for the interpretation of the sedimentation coefficients. All dsRNA segments of rotavirus (663-3409 base pairs) and the dsRNA5 of cucumber mosaic virus (335 base pairs) fit the model of a "worm-like" or flexible cylinder with a persistence length of 1125 A and a hydrated diameter of 30 A. The results are compared with data from the literature on the persistence lengths of the B- and Z-forms of dsDNA and of viroids.