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Mex67p, a novel factor for nuclear mRNA export, binds to both poly(A)+ RNA and nuclear pores
Abstract:
An essential cellular factor for nuclear mRNA export called Mex67p which has homologous proteins in human and Caenorhabditis elegans was identified through its genetic interaction with nucleoporin Nup85p. In the thermosensitive mex67-5 mutant, poly(A)+ RNA accumulates in intranuclear foci shortly after shift to the restrictive temperature, but NLS-mediated nuclear protein import is not inhibited. In vivo, Mex67p tagged with green fluorescent protein (GFP) is found at the nuclear pores, but mutant mex67-5-GFP accumulates in the cytoplasm. Upon purification of poly(A)+ RNA derived from of UV-irradiated yeast cells, Mex67p, but not nucleoporins Nup85p and Nup57p, was crosslinked to mRNA. In a two-hybrid screen, a putative RNA-binding protein with RNP consensus motifs was found to interact with the Mex67p carboxy-terminal domain. Thus, Mex67p is likely to participate directly in the export of mRNA from the nucleus to the cytoplasm.
Insights
Mex67p is a crucial protein for messenger RNA (mRNA) export from the nucleus. This study identifies Mex67p
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Nuclear mRNA export is a fundamental cellular process.
- Mex67p is a newly identified cellular factor involved in this process.
- Homologs of Mex67p exist in humans and C. elegans.
Purpose of the Study:
- To investigate the function of Mex67p in nuclear mRNA export.
- To elucidate the mechanism by which Mex67p facilitates mRNA transport.
- To identify interacting partners of Mex67p.
Main Methods:
- Genetic interaction studies with nucleoporin Nup85p.
- Analysis of poly(A)+ RNA localization in a thermosensitive mex67-5 mutant.
- In vivo localization of Mex67p tagged with green fluorescent protein (GFP).
- Biochemical crosslinking of Mex67p to mRNA.
- Two-hybrid screening to identify interacting proteins.
Main Results:
- The mex67-5 mutant shows poly(A)+ RNA accumulation in intranuclear foci at restrictive temperatures.
- Nuclear protein import remains unaffected in the mutant.
- Mex67p localizes to nuclear pores in vivo, while the mutant form accumulates in the cytoplasm.
- Mex67p, but not Nup85p or Nup57p, directly crosslinks to mRNA.
- A putative RNA-binding protein interacts with Mex67p.
Conclusions:
- Mex67p plays an essential role in nuclear mRNA export.
- Mex67p directly participates in the transport of mRNA from the nucleus to the cytoplasm.
- Mex67p likely functions by binding to mRNA and facilitating its translocation through nuclear pores.