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DNA Packaging

DNA Packaging

Lytic Cycle of Bacteriophages

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Bacteriophages, also known as phages, are specialized viruses that infect bacteria. A key characteristic of phages is their distinctive “head-tail” morphology. A phage begins the infection process (i.e., lytic cycle) by attaching to the outside of a bacterial cell. Attachment is accomplished via proteins in the phage tail that bind to specific receptor proteins on the outer surface of the bacterium. The tail injects the phage’s DNA genome into the bacterial cytoplasm. In the lytic replication...

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DNA Packaging

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Related Experiment Video

Updated: May 12, 2026

Isolation and Genome Analysis of Single Virions using 'Single Virus Genomics'

Isolation and Genome Analysis of Single Virions using 'Single Virus Genomics'

Published on: May 26, 2013

A promiscuous DNA packaging machine from bacteriophage T4.

Zhihong Zhang¹, Vishal I Kottadiel, Reza Vafabakhsh

¹Department of Biology, The Catholic University of America, Washington, District of Columbia, United States of America.

|March 2, 2011

Summary

The phage T4 packaging machine can package DNA into both empty and full virus heads, suggesting high conformational plasticity. This promiscuity may explain viral genome size evolution and enable new nanocapsid delivery vehicles.

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Isolation and Genome Analysis of Single Virions using 'Single Virus Genomics'

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T4 Bacteriophage and E. coli Interaction in the Murine Intestine: A Prototypical Model for Studying Host-Bacteriophage Dynamics In Vivo

T4 Bacteriophage and E. coli Interaction in the Murine Intestine: A Prototypical Model for Studying Host-Bacteriophage Dynamics In Vivo

Published on: January 26, 2024

Area of Science:

Molecular Biology
Virology
Biophysics

Background:

Complex viruses assemble from simple protein subunits through sequential processes.
Bacteriophage genome packaging involves a molecular motor at the portal vertex initiating DNA translocation into an empty prohead.
Capsid expansion and DNA cutting occur as the head fills, driven by conformational changes in the portal motor.

Purpose of the Study:

To investigate the packaging promiscuity and conformational plasticity of the phage T4 DNA packaging machine.
To determine if the packaging motor can translocate DNA into pre-filled or intact phage heads.
To explore the implications of these findings for viral genome evolution and nanobiotechnology.

Main Methods:

Utilized optical tweezers to measure the force and rate of DNA translocation by single phage T4 packaging motors.
Employed single-molecule fluorescence measurements to observe DNA packaging events and repeated initiations within phage heads.
Tested the ability of the packaging machine to translocate exogenous DNA into both proheads and finished phage heads.

Main Results:

The phage T4 packaging machine demonstrated high promiscuity, packaging DNA into both empty proheads and finished phage heads.
Single motors exhibited the same DNA translocation rate into both proheads and finished heads, indicating motor-driven packaging.
Phage heads underwent repeated packaging initiations, accommodating multiple DNA molecules, suggesting significant conformational plasticity.

Conclusions:

The phage DNA packaging machine possesses unusual conformational plasticity, actively driving DNA into a seemingly passive capsid.
This plasticity likely influenced the evolution of viral genomes fitting capsid volumes in double-stranded DNA viruses.
The findings suggest potential for designing novel nanocapsid delivery vehicles based on this mechanism.