The synthesis and transport of SV40 structural proteins

The kinetics of the synthesis and transport of viral structural proteins, Vp1 and Vp3, and of actin in SV40 infected TC7 cells were studied. The newly synthesized proteins were found in the NP-40-soluble (Sol) fraction of the cell cytoplasm. The majority of newly synthesized viral structural proteins, destined for the cell nucleus for virion assembly, were transported to the cell nucleus (Nuc) between 10 and 30 min after synthesis, whereas the majority of newly synthesized actin remained in the Sol fraction of the cytoplasm, suggesting that some specific mechanism exists for selecting the proper sites for transport. The synthesis and transport of both Vp1 and Vp3 throughout infected cells were similar. However, there is a difference in the transport properties of these two proteins. Once Vp1 was synthesized, the mature Vp1 was transported to both the cytoskeletal (Csk) and the Nuc fractions in the absence of further protein synthesis, whereas the movement of Vp3 from the Sol to the Csk, but not to the Nuc fraction, was partially inhibited in the absence of protein synthesis. Modification of Vp1 occurred in the cell cytoplasm before transport to the cell nucleus. Its modification pattern suggests that the Csk is the site for the modification of Vp1. The efficiency of viral protein transport to the cell nucleus was diminished after 47 hr of infection. This trend was preceded by a decrease in the ability to incorporate label into actin 12 hr earlier in infection. Thus, some marking event appears to have occurred prior to the actual decrease in transport efficiency and the integrity of the cytoarchitecture appears to be important for viral protein transport.