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Isolation of a polyoma-nucleoprotein complex from infected mouse-cell cultures
Abstract:
A complex containing polyoma (py) DNA and protein (py complex) was isolated from polyoma-infected mouse-cell cultures. The complex sedimented unimodally at about 55 S. When labeled for long periods (2-3 hr) between 20 and 40 hr after infection, most of the [(3)H]DNA in the py complex was in the form of covalently closed, circular polyoma DNA (component I). When labeled for 5 min, the [(3)H]DNA in the py complex was nicked in one or both of the strands, as shown by alkaline sucrose gradient centrifugation. Under all conditions studied, no free py DNA was extracted from mouse cells by the two methods described.
Insights
Researchers isolated a polyoma (py) DNA-protein complex from infected mouse cells. They found that newly synthesized polyoma DNA within this complex is initially circular and becomes nicked over time, indicating dynamic DNA processing.
Area of Science:
- Virology
- Molecular Biology
- Cellular Biology
Background:
- Polyoma virus (PyV) is a DNA tumor virus that infects various animal species.
- Understanding the replication and assembly of viral DNA within infected cells is crucial for virology research.
- Previous studies have focused on the structure of mature viral particles, but the dynamics of DNA within intracellular complexes are less understood.
Purpose of the Study:
- To characterize the structure and integrity of polyoma DNA within intracellular protein complexes.
- To investigate the state of newly synthesized polyoma DNA during the viral replication cycle.
- To determine if free polyoma DNA exists in infected mouse cells.
Main Methods:
- Isolation of polyoma DNA-protein complexes from infected mouse cell cultures.
- Sedimentation analysis (approx. 55 S) to characterize the complex.
- Radioactive labeling of DNA ([(3)H]DNA) for short (5 min) and long (2-3 hr) periods.
- Alkaline sucrose gradient centrifugation to assess DNA strand integrity.
Main Results:
- A stable polyoma DNA-protein complex (approx. 55 S) was isolated.
- Long-term labeling revealed predominantly covalently closed, circular polyoma DNA (component I) within the complex.
- Short-term labeling demonstrated that newly synthesized DNA in the complex was often nicked in one or both strands.
- No free polyoma DNA was detected in infected cells using the employed extraction methods.
Conclusions:
- Newly synthesized polyoma DNA undergoes processing within intracellular protein complexes.
- The DNA within the polyoma complex transitions from a nicked state to a covalently closed circular form.
- The study provides evidence against the existence of significant amounts of free polyoma DNA in infected mouse cells.