Exploring the architecture of the intact supraspliceosome using electron microscopy

Area of Science:

• Molecular Biology
• Structural Biology
• Cell Biology

Background:

• Pre-mRNA splicing occurs in eukaryotic cells via the supraspliceosome, a large macromolecular machine.
• The supraspliceosome comprises four native spliceosomes, each with two distinct subunits.
• Previous structural studies lacked detail on native spliceosome arrangement within the intact supraspliceosome.

Purpose of the Study:

• To determine the arrangement of native spliceosomes within the intact supraspliceosome.
• To elucidate the structural organization and subunit roles in supraspliceosome function.
• To identify the pathway of pre-mRNA through the supraspliceosome.

Main Methods:

• Electron microscopy combined with image processing.
• Analysis and reconstruction of native spliceosomes within the intact particle.
• Comparison with cryo-electron microscopy (cryo-EM) data of isolated native spliceosomes.

Main Results:

• A strong correlation was found between isolated and integrated native spliceosome structures.
• An ordered assembly of native spliceosomes was revealed within the supraspliceosome.
• The small subunits form a central, right-angled structure, creating a 4-fold pattern, suggesting specific functional roles and a pre-mRNA passage route.

Conclusions:

• The supraspliceosome exhibits an ordered arrangement of native spliceosomes with distinct subunit functions.
• The structural findings provide insights into the mechanism of pre-mRNA splicing and transport.
• This study advances our understanding of the supraspliceosome's architecture and function in gene expression.