Recently replicated simian virus 40 DNA is a preferential template for transcription and replication

Area of Science:

• Molecular Biology
• Virology

Background:

• Simian virus 40 (SV40) DNA replication and transcription are crucial for viral propagation.
• Understanding the template activity of newly synthesized versus uniformly labeled DNA is key to deciphering viral gene expression dynamics.

Purpose of the Study:

• To compare the template activities of recently replicated ("new") and uniformly labeled ("old") SV40 DNA for replication and transcription.
• To investigate the role of replicating viral genomes in initiating late transcription.

Main Methods:

• Pulse-labeling and long-term labeling of SV40 DNA in infected monkey cells (TC7).
• Assessing template activity for replication by measuring DNA synthesis rates.
• Quantifying RNA polymerase association with replicated and non-replicated viral DNA using Triton-soluble transcription complexes.

Main Results:

• "New" SV40 DNA served as a replication template with high probability for 5 hours before activity decreased; "old" DNA showed constant, lower template activity for at least 12 hours.
• Late transcription initiation did not require replicating viral genomes, as RNA synthesis was associated with covalently closed circular DNA.
• Recently replicated viral DNA exhibited nearly three times more associated RNA polymerase per unit DNA than non-replicated DNA after 9 hours.

Conclusions:

• Recently replicated SV40 DNA is preferentially utilized as a template for both subsequent replication and transcription.
• This preferential use of new DNA suggests a dynamic regulation of viral genome template activity during infection.