Fluctuation Pressure Assisted Ejection of DNA From Bacteriophage

TL;DR

This paper models how thermal pressure fluctuations within tightly packed DNA generate significant internal pressure that can assist in ejecting DNA from bacteriophage capsids, supported by comparisons with experimental data.

Contribution

It introduces a model calculating thermal pressure fluctuations in DNA bundles inside phages, highlighting their potential role in facilitating DNA ejection.

Findings

Pressure fluctuations reach tens of atmospheres in small phages

Thermal vibrations can significantly contribute to DNA ejection pressure

Model aligns with experimental measurements on lambda phage mutants

Abstract

The role of thermal pressure fluctuation excited within tightly packaged DNA prior to ejection from protein capsid shells is discussed in a model calculation. At equilibrium before ejection we assume the DNA is folded many times into a bundle of parallel segments that forms an equilibrium conformation at minimum free energy, which presses tightly against internal capsid walls. Using a canonical ensemble at temperature T we calculate internal pressure fluctuations against a slowly moving or static capsid mantle for an elastic continuum model of the folded DNA bundle. It is found that fluctuating pressure on the capsid internal wall from thermal excitation of longitudinal acoustic vibrations in the bundle may have root-mean-square values which are several tens of atmospheres for typically small phage dimensions. Comparisons are given with measured data on three mutants of lambda phage with different base pair lengths and total genome ejection pressures.