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Updated: Feb 11, 2026
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Single-Molecule Real-Time Visualization of DNA Unwinding by CMG Helicase
Published on: September 27, 2024
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Real-time observations of single bacteriophage lambda DNA ejections in vitro.
Paul Grayson1, Lin Han, Tabita Winther
1Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.
Summary
Bacteriophage genome ejection speed was measured in real-time. Genome length and ionic conditions significantly impact DNA translocation speed and duration, offering insights into viral DNA packaging and release mechanisms.
Area of Science:
- Molecular Biology
- Biophysics
- Virology
Background:
- Bacteriophage genome release mechanisms are under active investigation.
- Previous studies focused on internal forces and observed stepwise DNA ejection in phage T5.
- The precise speed and influencing factors of bacteriophage DNA translocation remain largely unknown.
Purpose of the Study:
- To investigate the real-time kinetics of bacteriophage lambda genome ejection.
- To determine the dependence of ejection speed on physical parameters like genome length and buffer ionic composition.
- To elucidate the role of internal pressure and friction in DNA translocation.
Main Methods:
- Real-time measurements of bacteriophage lambda DNA ejection.
- Systematic variation of genome length and ionic conditions (sodium vs. magnesium ions).
- Analysis of translocation speed and total ejection time.
Main Results:
- Phage lambda translocates its 48.5-kbp genome in approximately 1.5 seconds at speeds up to 60 kbp/s, with a brief pause before final release.
- Shorter genome lengths decrease translocation speed but reduce overall ejection time.
- Divalent magnesium ions significantly slow down ejection (8-11 seconds) compared to monovalent ions, indicating reduced internal pressure.
- Tighter DNA packing within the phage head leads to earlier initiation but lower initial ejection speed due to increased friction.
Conclusions:
- The study provides precise measurements of bacteriophage DNA ejection speed and its dependence on physical parameters.
- Internal DNA pressure and friction are critical factors influencing the initiation and speed of genome translocation.
- These findings offer insights into the generic mechanisms of DNA translocation in bacteriophages and potentially other biological systems.
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