AT-specific DNA visualization revisits the directionality of bacteriophage λ DNA ejection

Area of Science:

• Molecular Biology
• Structural Biology
• Biophysics

Background:

• Phage DNA packaging and ejection are crucial for viral infection.
• The prevailing Last In First Out (LIFO) model assumes unidirectional ejection.
• Limited understanding of DNA dynamics within the confined phage capsid.

Purpose of the Study:

• To investigate the mechanism and probability of DNA end selection during in vitro phage ejection.
• To challenge or support the established Last In First Out (LIFO) model.
• To explore the mobility of DNA within a highly condensed phage capsid.

Main Methods:

• AT-specific visualization of DNA molecules during in vitro phage ejection.
• Computer simulations to model DNA behavior and ejection dynamics.
• Analysis of ejected DNA length in relation to ejection models (LIFO vs. FIFO).

Main Results:

• Observed nearly 50% probability for ejection starting from either DNA end, contradicting LIFO.
• Computer simulations confirmed randomized DNA end selection.
• Ejected DNA length differed between LIFO and First In First Out (FIFO) models, attributed to DNA stiffness.

Conclusions:

• The study demonstrates that DNA molecules exhibit mobility within dense phage capsids.
• DNA can switch ends during ejection, leading to a near 50% probability for either end initiating the process.
• Findings necessitate a revision of current models for phage DNA ejection dynamics.