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The mRNA export factor Dbp5 is associated with Balbiani ring mRNP from gene to cytoplasm
Jian Zhao1, Shao-Bo Jin, Birgitta Björkroth
1Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, SE-17177 Stockholm, Sweden.
Abstract:
The DEAD box RNA helicase Dbp5 is essential for nucleocytoplasmic transport of mRNA-protein (mRNP) complexes. Dbp5 is present mainly in the cytoplasm and is enriched at the cytoplasmic side of nuclear pore complexes (NPCs), suggesting that it acts in the late part of mRNP export. Here, we visualize the assembly and transport of a specific mRNP particle, the Balbiani ring mRNP in the dipteran Chironomus tentans, and show that a Dbp5 homologue in C.tentans, Ct-Dbp5, binds to pre-mRNP co-transcriptionally and accompanies the mRNP to and through the nuclear pores and into the cytoplasm. We also demonstrate that Ct-Dbp5 accumulates in the nucleus and partly disappears from the NPC when nuclear export of mRNA is inhibited. The fact that Ct-Dbp5 is present along the exiting mRNP fibril extending from the nuclear pore into the cytoplasm supports the view that Ct-Dbp5 is involved in restructuring the mRNP prior to translation. Finally, the addition of the export factor Dbp5 to the growing transcript highlights the importance of the co-transcriptional loading process in determining the fate of mRNA.
Insights
The DEAD box RNA helicase Dbp5 binds mRNA co-transcriptionally and accompanies it through nuclear pores. This RNA helicase is crucial for mRNA export and restructuring mRNPs for translation.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- The DEAD box RNA helicase Dbp5 is vital for mRNA-protein (mRNP) complex export from the nucleus.
- Dbp5 localizes to the cytoplasm and nuclear pore complexes (NPCs), suggesting a role in late-stage mRNP export.
Purpose of the Study:
- To visualize the assembly and transport of Balbiani ring mRNPs in Chironomus tentans.
- To investigate the role of the Dbp5 homologue, Ct-Dbp5, in mRNP biogenesis and export.
Main Methods:
- Live-cell imaging of mRNP particles during transcription and export.
- Inhibition of nuclear mRNA export to observe Ct-Dbp5 localization changes.
Main Results:
- Ct-Dbp5 binds to pre-mRNPs during transcription and travels with them to and through the NPC.
- Ct-Dbp5 accumulates in the nucleus and diminishes at the NPC upon inhibition of mRNA export.
- Ct-Dbp5 is present on mRNP fibrils exiting the NPC into the cytoplasm.
Conclusions:
- Ct-Dbp5 plays a role in the co-transcriptional loading and nuclear export of mRNPs.
- Dbp5 is involved in restructuring mRNPs for subsequent translation.
- Co-transcriptional loading is critical for determining mRNA fate.