Adenovirus replication and transcription sites are spatially separated in the nucleus of infected cells.

We have visualized the intranuclear topography of adenovirus replication and transcription in infected HeLa cells. The results show that viral DNA replication occurs in multiple foci that are highly organized in the nucleoplasm. Pulse-chase experiments indicate that newly synthesized viral double-stranded DNA molecules are displaced from the replication foci and spread throughout the nucleoplasm, while the single-stranded DNA replication intermediates accumulate in adjacent sites. Double-labelling experiments and confocal microscopy show that replication occurs in foci localized at the periphery of the sites where single-stranded DNA accumulates. The simultaneous visualization of viral replication and transcription reveals that the sites of transcription are predominantly separated from the sites of replication. Transcription is detected adjacent to the replication foci and extends around the sites of single-stranded DNA accumulation. These data indicate that newly synthesized double-stranded DNA molecules are displaced from the replication foci and spread in the surrounding nucleoplasm, where they are used as templates for transcription. Splicing snRNPs are shown to co-localize with the sites of transcription and to be excluded from the sites of replication. This provides evidence that splicing of viral RNAs occurs co-transcriptionally and that the sites of viral DNA replication are spatially distinct from the sites of RNA transcription and processing.