The relationship between the components of cowpea mosaic virus: II. Further characterization of the nucleoprotein components of CPMV

Abstract

The large-scale separation and purification of the nucleoprotein components of cowpea mosaic virus by means of zonal centrifugation in a B XIV zonal rotor is described. The component with a sedimentation coefficient of 95 S, referred to as middle component, could be obtained free of infectivity after two runs in the zonal rotor. The so-called bottom component, with a sedimentation coefficient of 115 S, had to be subjected to equilibrium density gradient centrifugation in 40% (w/w) CsCl in order to eliminate middle component completely and to obtain it free of infectivity. The infectivity of the virus could be restored by mixing middle and bottom components. There was no appreciable effect of the purification procedure on the biological activity of the components. Bottom component gave two bands in CsCl density gradients. The band with the greater buoyant density appears to be the unaffected bottom component; the lighter one is an artifact of CsCl centrifugation. The sedimentation coefficients of the RNA of each component have been determined, and the molecular weights have been calculated. The buoyant density of the RNA in cesium sulfate is 1.627 g/cm 3. The base compositions of middle and bottom component RNA were determined after alkaline hydrolysis. Bottom component RNA has more guanylic acid and less cytidylic acid than the RNA of middle component.