Ratcheting mRNA out of the nucleus

Area of Science:

• Molecular Biology
• Cell Biology
• Eukaryotic Gene Expression

Background:

• Nuclear mRNA export is a critical step in eukaryotic gene expression, culminating in the transport of mature messenger ribonucleoprotein (mRNP) complexes to the cytoplasm.
• The Mex67:Mtr2 heterodimer plays a crucial role in facilitating the passage of these export-competent mRNPs through the nuclear pore complexes (NPCs).

Purpose of the Study:

• To elucidate the mechanism of mRNP remodeling at the cytoplasmic face of the NPC, which ensures directional transport and prevents nuclear reentry.
• To investigate the role of the DEAD-box helicase Dbp5 in mRNP remodeling and its regulation by Gle1 and inositol hexaphosphate (IP(6)).

Main Methods:

• Studies were conducted in budding yeast.
• Investigated the function of the Mex67:Mtr2 complex in NPC passage.
• Examined the activity of the DEAD-box helicase Dbp5, including its interaction with Gle1 and IP(6).

Main Results:

• Mex67:Mtr2 facilitates mRNP transport through NPCs.
• mRNP remodeling at the cytoplasmic face of the NPC acts as a molecular ratchet, ensuring unidirectional export.
• The DEAD-box helicase Dbp5 remodels mRNPs by removing Mex67 at the NPC cytoplasmic face, with its ATPase activity activated by Gle1 and IP(6).

Conclusions:

• Dbp5, activated by Gle1 and IP(6), is a key regulator of mRNP remodeling at the NPC cytoplasmic face.
• This remodeling process is essential for imposing directionality on mRNA export, preventing its return to the nucleus.
• The findings provide insights into the molecular mechanisms governing the final stages of nuclear mRNA export in eukaryotes.