The isolation of ribonuclease - resistant RNA induced by cowpea mosaic virus: evidence for two double - stranded RNA components

Purified infectious preparations of cowpea mosaic virus consist of three centrifugal components with sedimentation coefficients of 58, 95 and 115S. These are referred to as top, middle and bottom component and contain 0, 23 and 34% RNA respectively (van Kammen, 1967). All three components are isometric particles with a diameter of 28 nm. and have serologically similar capsids. Recently van Kammen (1968) demonstrated that both RNA-containing components of the virus are necessary for infection. RNA prepared from purified middle component and bottom component is homogeneous in the analytical ultracentrifuge (u.v. optics) and has sedimentation coefficients of 26S and 34S respectively (L. J. L. D. van Griensven & A. van Kammen, unpublished). By applying Spirin's (1963) relationship between the molecular weight of an RNA and its sedimentation coefficient (Mol. Wt = 1550 × S 2.1) the molecular weights were calculated as 1.4 × 106 and 2.5 × 106 respectively.