Structure of simian virus 40 II. Symmetry and components of the virus particle

The symmetry of SV40 particles was examined and proved to be the T = 7 icosahedral surface lattice. Evidence is presented that the three types of shells of smaller size are derived from reassembled morphological units of normal particle shells. Examination of the surface structure of the smaller particles strongly suggested icosahedral surface lattices of T = 3 , T = 3, and T = 4 symmetry classes. Three different polypeptide chains with an average molecular weight of 16,350 ± 10% were identified in the protein moiety of the virus particle. The proportion was determined as 45.5 : 45.5 : 9. Four different approaches were used to determine the size of the virus DNA. A molecular weight of 2.25 × 10 6 ± 15% was established. A calculation of the particle weight from the size and number of the components yielded 17.3 × 10 6 ± 10%.