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Updated: Jul 14, 2026
09:40
Phage Phenomics: Physiological Approaches to Characterize Novel Viral Proteins
Published on: June 11, 2015
Ionic effects on viral DNA packaging and portal motor function in bacteriophage phi 29
Derek N Fuller1, John Peter Rickgauer, Paul J Jardine
1Department of Physics, University of California, San Diego, Mail Code 0379, 9500 Gilman Drive, La Jolla, CA 92093, USA.
Summary
Viral DNA packaging requires overcoming electrostatic repulsion. This study reveals how ions like Mg(2+) and Na(+) influence DNA confinement forces and motor function in bacteriophage phi 29 packaging dynamics.
Area of Science:
- Biophysics
- Molecular Biology
- Virology
Background:
- Viral DNA packaging involves confining large amounts of DNA into a small capsid, facing energy barriers from DNA bending and electrostatic repulsion.
- Powerful molecular motors are essential for overcoming these barriers during viral assembly.
Purpose of the Study:
- To investigate the impact of electrostatic repulsion and ion conditions on the dynamics of single DNA packaging in bacteriophage phi 29.
- To differentiate the effects of ions on DNA packing forces versus motor function.
Main Methods:
- Utilized optical tweezers to perform single DNA packaging measurements in bacteriophage phi 29.
- Employed constant force and velocity versus load measurements under varying ionic conditions and capsid filling levels.
Main Results:
- Ionic screening significantly affects DNA packing forces, confirming the role of electrostatic repulsion.
- Magnesium ions (Mg(2+)) are crucial for initiating packaging; sodium ions (Na(+)) enhance motor velocity.
- DNA confinement forces were substantially higher with Na(+) as the dominant ion, limiting packaging efficiency.
Conclusions:
- Electrostatic repulsion is a major factor in viral DNA packaging, modulated by ion type and concentration.
- Current models underestimate the forces involved in DNA confinement within viral capsids.
- Understanding ion-mediated forces is critical for comprehending viral assembly mechanisms.
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