ASSOCIATION WITH CAPSID PROTEINS PROMOTES NUCLEAR TARGETING OF SIMIAN-VIRUS-40 DNA

All animal DNA viruses except pox virus utilize the cell nucleus as th e site for virus reproduction. Yet, a critical viral infection process , nuclear targeting of the viral genome, is poorly understood, The rol e of capsid proteins in nuclear targeting of simian virus 40 (SV40) DN A, which is assessed by the nuclear accumulation of large tumor (T) an tigen, the initial sign of the infectious process, was tested by two i ndependent approaches: antibody interception experiments and reconstit ution experiments. When antibody against viral capsid protein Vp1 or V p3 was introduced into the cytoplasm, the nuclear accumulation of T an tigen was nor observed in cells either infected or cytoplasmically inj ected with virion. Nuclearly introduced anti-T-Vp3 IgG also showed the inhibitory effect. In the reconstitution experiments, SV40 DNA was al lowed to interact with protein components of the virus, either empty p articles or histones, and the resulting complexes were tested for the capability of protein components to target the DNA to the nucleus from cytoplasm as effectively as the targeting of DNA in the mature virion , In cells injected with empty particle-DNA, but not in minichromosome -injected cells, T antigen was observed as effectively as in SV40-inje cted cells, These results demonstrate that SV40 capsid proteins can fa cilitate transport of SV40 DNA into the nucleus and indicate that Vp3, one of the capsid proteins, accompanies SV40 DNA as it enters the nuc leus during virus infection.