Asymmetric cryo-EM reconstruction of phage MS2 reveals genome structure in situ

Area of Science:

• Virology
• Structural Biology
• Molecular Biology

Background:

• Virus capsid assembly and genome packaging are complex, interconnected processes in single-stranded RNA viruses.
• Understanding these mechanisms is crucial for developing antiviral strategies and gene therapy vectors.

Purpose of the Study:

• To determine the asymmetric virion structure of bacteriophage MS2 using advanced imaging techniques.
• To elucidate the role of the viral RNA genome in the assembly and packaging of bacteriophage MS2.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to capture high-resolution images of the virion.
• Single particle analysis was used to reconstruct the three-dimensional structure of the bacteriophage MS2 virion.

Main Results:

• The asymmetric structure of bacteriophage MS2 was determined, revealing 178 coat protein copies and one A-protein copy encapsidating the RNA genome.
• The viral RNA genome was observed to adopt a specific, branched stem-loop conformation within the capsid.
• The RNA predominantly interacted with coat protein dimers located on one side of the capsid, near its inner surface.

Conclusions:

• The viral RNA genome is not merely a passive cargo but actively participates in bacteriophage MS2 assembly and genome packaging.
• The specific RNA conformation and its interaction with coat proteins provide insights into the mechanism of viral morphogenesis.