SV40 VP1 assembles into disulfide-linked postpentameric complexes in cell-free lysates.

The simian virus 40 (SV40) capsid is composed of pentameric capsomeres of the major structural protein, Vp1. The chemical nature of Vp1-Vp1 interactions, as well as the role of the minor structural proteins, Vp2 and Vp3, in SV40 assembly is not clear. We show here that Vp1 molecules synthesized in rabbit reticulocyte lysates self-assembled into postpentameric 12S complexes in the absence of other viral structural proteins and in a time and concentration dependent manner. The 12S complexes were resistant to perturbants of noncovalent interactions but were sensitive to reduction by dithiothretiol. Nonreducing SDS-PAGE analysis revealed disulfide-linked VP1 complexes of > 400 kDa. Our results are consistent with crystallography studies of SV40 which suggest involvement of disulfide bonds at a postcapsomeric stage of viral assembly.