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Viroid replication: equilibrium association constant and comparative activity measurements for the viroid-polymerase
Nucleic Acids Research
|August 10, 1984
Summary
Wheat germ DNA-dependent RNA polymerase II binds potato spindle tuber viroid (PSTV) with high affinity. Two distinct viroid-polymerase complexes (1:1 and 2:1 stoichiometry) were identified, suggesting complex interactions crucial for viroid replication.
Area of Science:
- Molecular Biology
- Virology
- Biochemistry
Background:
- Viroids are small, circular RNA molecules that replicate independently of viruses.
- Understanding the interaction between viroids and host cell machinery is crucial for deciphering their replication mechanisms.
Purpose of the Study:
- To investigate the binding and replication of potato spindle tuber viroid (PSTV) by DNA-dependent RNA polymerase II (Pol II) from wheat germ.
- To characterize the stoichiometry and nature of viroid-polymerase complexes.
Main Methods:
- Analytical ultracentrifugation experiments.
- In vitro transcription assays.
- UV and fluorescence monitoring during sedimentation.
- Electron microscopy.
Main Results:
- High equilibrium association constant (1.9 X 10(7) M-1) for PSTV-Pol II interaction.
- Identification of two distinct viroid-polymerase complexes, indicating 1:1 and 2:1 enzyme-to-viroid binding stoichiometry.
- Sedimentation velocity and A265/A280 ratios supported the complex stoichiometry.
Conclusions:
- Wheat germ Pol II binds PSTV with high affinity, forming distinct complexes.
- The results suggest a role for viroid secondary structure in enzyme binding and polymerization.
- Comparison with other nucleic acids highlights unique viroid-polymerase interactions.