Genome organization in double-stranded DNA viruses observed by cryoET

Area of Science:

• Structural biology
• Virology
• Biophysics

Background:

• Double-stranded DNA (dsDNA) viruses compress large genomes into small capsids, a process that is energetically demanding and poorly understood.
• Existing models of viral DNA packaging lack direct visualization of the genome's internal organization.
• Understanding dsDNA packaging is crucial for comprehending viral replication and developing antiviral strategies.

Approach:

• Utilized cryo-electron tomography (cryoET) combined with an advanced data processing technique leveraging capsid protein shell information.
• Achieved high-resolution 3D imaging of dsDNA genomes within individual viral particles, enabling visualization of individual DNA duplexes.
• Examined herpes simplex virus type 1 (HSV-1), bacteriophage T4, and bacteriophage T7 to identify conserved genome structures.

Key Points:

• Direct 3D visualization of dsDNA genomes inside viral capsids at unprecedented resolution.
• Identified a conserved "rod-and-coil" folding motif for dsDNA across diverse virus types (HSV-1, T4, T7).
• The observed genome organization provides insights into the physical constraints and mechanisms of viral DNA packaging.

Conclusions:

• The "rod-and-coil" structure represents a fundamental principle of dsDNA genome organization within viruses.
• Partially packaged bacteriophage T4 particles inspired a novel proposed mechanism for dsDNA genome packaging.
• This study provides critical structural data to refine models of viral DNA packaging and inform future research.