Capsid buoyant density

Sedimentation coefficient 155 Buoyant density (CsCl) 1.34 g/ml Virions stable at pH 3-10 Empty capsids produced in vivo... 

Sedimentation coefficient a/155 S Buoyant density vl.40 g/ml Virions labile pH- 5 Empty capsids produced j n vivo... 

The remarkable difference in buoyant density between the entero- and cardioviruses (l.34g/nil) and FMUV (l.45g/nil) can best be explained by the difference in penetration of the Cs ions and subsequent reaction with the ENA. If we accept values for the density of empty capsids and ENA of I.JOg/ml and 1.91g/ml respectively we can calculate that the density of a particle containing 50% ENA and 7C% protein should be 1.48g/ml. This calculation will only be valid, however, if the ENA and protein react completely with the Os " ions. Clearly the ENA in the entero- and cardioviruses must be protected from reaction with the Cs ions by its interaction with the virus protein. Even the FMUV particle has a buoyant density less than the theoretical maximiun. 

AAV is usually recovered from infected cells using trypsin and deoxy-cholate. Sedimentation in CsCl leads to a major AAV band at a buoyant density of 1.40 g/cm and a minor band at 1.467 g/cm. When sarkosyl was substituted for deoxycholate, the major AAV band in CsCl occurred at the same density as that of AAV purified in the usual manner. However, the amount of material in the denser minor band was increased. Virions in the minor band have been characterized as being smaller than AAV and probably have had some of the capsid stripped away (Hoggan, 1971). After sarkosyl treatment even the AAV from the major normal density band in CsCl was unable to adsorb to KB cells (less than 10% of normal) implying that an intact capsid is required for adsorption (Berns and Adler, unpublished data). 

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