Virus Propagation Linked to Exceedingly Rare Gene-Expression Errors: A Single-Molecule Microscopy Demonstration.

Area of Science:

• Virology
• Molecular Biology
• Evolutionary Biology

Background:

• Viruses often employ complex RNA mechanisms for high-level protein synthesis.
• Gene expression errors, though typically inefficient, may offer survival benefits.
• Phage T7 relies on host thioredoxin as a crucial DNA polymerase processivity factor.

Purpose of the Study:

• To experimentally demonstrate that viruses can survive and replicate with extremely low protein levels.
• To investigate the molecular and evolutionary implications of low-abundance proteins in viral replication.
• To explore how gene expression errors might facilitate viral adaptation and cross-species transmission.

Main Methods:

• Engineered bacteriophage T7 with stop codons in the thioredoxin gene and fused it to a fluorescent protein.
• Utilized single-molecule localization microscopy to quantify thioredoxin levels during phage replication.
• Analyzed the kinetic stability and residence time of the polymerase-thioredoxin complex.

Main Results:

• Phage T7 replicated efficiently even with an average of only ~10 thioredoxin molecules per host cell.
• Replication was sustained despite protein levels orders of magnitude lower than typical cellular concentrations.
• High kinetic stability and long residence time of the polymerase-thioredoxin complex explained the observed efficiency.

Conclusions:

• Viral replication can be sustained by proteins present at exceptionally low copy numbers.
• Gene expression errors generate diverse protein variants that can confer a survival advantage.
• This mechanism may be critical for viral survival in new hosts prior to genetic adaptation.