Eukaryotic initiation factor 3 does not prevent association through physical blockage of the ribosomal...

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• The 40 S ribosomal subunit is crucial for protein synthesis.
• Eukaryotic initiation factor 3 (eIF3) is a large protein complex that binds the 40 S subunit.
• The precise role and binding site of eIF3 on the 40 S subunit are not fully understood.

Purpose of the Study:

• To determine the three-dimensional structure of the native 40 S ribosomal subunit with bound eukaryotic initiation factor 3.
• To elucidate the attachment site and morphology of eIF3 on the 40 S subunit.
• To gain insights into the anti-association activity of eIF3.

Main Methods:

• Three-dimensional reconstruction of the native 40 S ribosomal subunit.
• Cryo-electron microscopy at 48 A resolution.
• Comparison with a derived 40 S subunit lacking non-ribosomal components.

Main Results:

• The native 40 S ribosomal subunit with bound eukaryotic initiation factor 3 was reconstructed to 48 A resolution.
• Eukaryotic initiation factor 3 is a large, bilobed, elongate structure (165-170 A long).
• eIF3 attaches to the back lobes of the 40 S subunit via two strand-like features, oriented away from the subunit interface.

Conclusions:

• The study reveals the precise attachment site and morphology of eukaryotic initiation factor 3 on the 40 S ribosomal subunit.
• The orientation of eIF3 suggests its anti-association activity is not due to simple physical blockage of the subunit interface.
• This structural information provides a basis for understanding eIF3's function in translation initiation.