Synthesis of full-length, virus genomic DNA by nuclei of vaccinia-infected HeLa cells.

It is well established that vaccinia virus infection induces the synthesis of virus-specific DNA in cytoplasmic 'factories', which are sites of virus-specific transcription. The present study demonstrates that vaccinia virus-specific DNA is synthesized also in the nuclei of infected cells with a similar time course. Direct observation and radiolabelling confirm the integrity of isolated nuclei. Reconstitution experiments and inhibitor studies demonstrate that virus-induced DNA is synthesized de novo within nuclei and does not result from cytoplasmic contamination. Cell-specific DNA synthesis is inhibited completely after infection and nuclei of infected cells then synthesize DNA which co-sediments with virus genomic DNA in denaturing gradients. Restriction endonuclease cleavage and hybridization with a virus-specific probe indicate that this is full-length, virus genomic DNA. The biological implications of this are discussed.