Splicing is required for rapid and efficient mRNA export in metazoans

Area of Science:

• Molecular Biology
• Cell Biology
• Gene Expression

Background:

• Pre-mRNA splicing is a critical nuclear process preceding mRNA export.
• The biochemical coupling between mRNA splicing and export remains largely unknown.
• Introns are often required for efficient gene expression in metazoans.

Purpose of the Study:

• To investigate whether pre-mRNA splicing and mRNA export are biochemically coupled.
• To determine if splicing influences the efficiency and mechanism of mRNA export.

Main Methods:

• Injection of pre-mRNAs with and without introns into Xenopus oocyte nuclei.
• Competition assays using intron-less mRNAs (Deltai-mRNAs).
• In vitro assembly of messenger ribonucleoprotein particles (mRNPs) from spliced and unspliced mRNAs.

Main Results:

• Spliced mRNAs were exported more rapidly and efficiently than identical intron-less mRNAs (Deltai-mRNAs).
• Competition studies suggested distinct factors mediate the export of spliced versus Deltai-mRNAs.
• Spliced and Deltai-mRNAs formed different mRNPs in vitro, with only spliced mRNA-containing mRNPs exported efficiently.

Conclusions:

• Splicing generates a specific nucleoprotein complex that targets mRNA for export.
• A direct link exists between mRNA splicing and efficient mRNA export.
• This coupling may explain the requirement of introns for efficient gene expression.