Does simian virus 40 DNA integrate into cellular DNA during productive infection?

Area of Science:

• Virology
• Molecular Biology
• Genetics

Background:

• Simian virus 40 (SV40) infection of monkey cells leads to large amounts of viral DNA associated with high-molecular-weight cellular DNA.
• Previous studies suggested this SV40 DNA is covalently integrated into the host cell genome.

Purpose of the Study:

• To investigate the nature of SV40 DNA found in the high-molecular-weight fraction of infected monkey cells.
• To determine if SV40 DNA is integrated into the host genome or exists in a different form.

Main Methods:

• Analysis of SV40 DNA size and structure using agarose gel electrophoresis.
• Digestion with restriction endonucleases (EcoRI, HpaII, and others targeting cellular DNA).
• Heteroduplex formation with marker viral DNA and hybridization studies.

Main Results:

• SV40 DNA in the high-molecular-weight fraction exists as tandem, head-to-tail repeats (polymers) larger than 45 kilobases.
• Over 95% of SV40 DNA was released as unit-length linear molecules after digestion with SV40-specific endonucleases, indicating lack of integration.
• Cellular DNA-specific enzymes did not affect the SV40 DNA polymers.
• Polymeric SV40 DNA is highly infectious and efficiently converted to monomeric circular DNA in host cells.

Conclusions:

• The high-molecular-weight SV40 DNA is not covalently integrated into cellular DNA but exists as infectious tandem repeats.
• Host cells possess an efficient mechanism for converting these SV40 DNA polymers into infectious monomeric circular viral DNA.