The organization of mature Rous sarcoma virus as studied by cryoelectron microscopy

Area of Science:

• Virology
• Structural Biology
• Electron Microscopy

Background:

• Rous sarcoma virus (RSV) is a retrovirus with implications for cancer research.
• Understanding the structural organization of infectious virions is crucial for deciphering viral replication and assembly.

Purpose of the Study:

• To elucidate the three-dimensional organization of mature, infectious Rous sarcoma virus (RSV) particles.
• To characterize the morphology and dimensions of the viral core and its relationship to the overall virion size.

Main Methods:

• Transmission electron microscopy (TEM) of RSV suspended in vitreous ice.
• Advanced image processing techniques to analyze viral structure.
• Geometric probability methods to estimate core dimensions from projection data.

Main Results:

• RSV virions are spherical with a mean diameter of 127 nm, exhibiting size variability.
• The viral matrix protein is located beneath the lipid bilayer, with envelope proteins on the exterior.
• The retroviral core is essentially isometric, unlike lentiviruses, and displays a faceted or curved capsid structure.
• Core size is not tightly regulated and correlates positively with virion size.
• Serrations on the core suggest a repetitive molecular arrangement.
• Isolated cores demonstrate transient stability.

Conclusions:

• The study provides detailed structural insights into Rous sarcoma virus organization.
• Core size variability and its correlation with virion size suggest a flexible assembly process.
• The data indicate that the viral RNA may be loosely packed or does not occupy the entire core volume.