Localization of eukaryotic initiation factor 3 on native small ribosomal subunits

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Ribosomes are essential for protein synthesis.
• Eukaryotic initiation factor 3 (eIF-3) plays a critical role in translation initiation.
• The precise localization of eIF-3 on ribosomal subunits is not fully understood.

Purpose of the Study:

• To determine the localization of eukaryotic initiation factor 3 (eIF-3) on native small ribosomal subunits.
• To visualize the structural impact of eIF-3 binding to 40S ribosomal subunits.

Main Methods:

• Electron microscopy was used to compare native small ribosomal subunits, derived subunits, and subunits stripped of eIF-3.
• Reticulocyte ribosomes were treated with puromycin/KCl to derive small subunits.
• High salt concentrations were used to remove eIF-3 from native subunits.

Main Results:

• Native small ribosomal subunits typically exhibit a three-lobed appearance due to an attached mass (eIF-3).
• Derived small subunits and eIF-3-stripped subunits appear as elongated particles without the additional mass.
• The attached mass, identified as eIF-3, is located on a central prominence of the small subunit.

Conclusions:

• Eukaryotic initiation factor 3 (eIF-3) binds to native small ribosomal subunits.
• The binding of eIF-3 alters the morphology of the small ribosomal subunit, creating a three-lobed structure.
• This structural change mediated by eIF-3 is important for its role in translation initiation.