On the size of the protein subunits in bushy stunt virus

Bushy stunt virus was degraded extensively to produce slowly sedimenting material together with small amounts of more rapidly sedimenting materials. By means of high-speed centrifugation the smaller products were separated from the larger products; repeated salting out of the protein in the smaller products, by means of ammonium sulfate, gave a preparation showing the spectrum of a purified protein. Since the degradation of the virus was effected by means of dilute sodium dodecyl sulfate without resort to extremes of pH or temperature, it is likely that there was no rupture of covalent bonds. The resultant protein can then be considered as molecular subunits of the virus which, before degradation, were held together by secondary forces to form the organized structure characteristic of the virus particles. The molecular weight of the protein was determined by a direct ultracentrifugal method involving the approach to sedimentation equilibrium. In a system containing protein and detergent, ultracentrifugal analysis is complicated by interactions among the various components; potential sources of error inherent in such experiments are assessed. Analysis of the data showed that the molecular weight of the protein subunit produced by this treatment was 6 × 10 4 and the intact virus particles were composed of about 120 such units along with the ribonucleic acid.