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Rna1p, a Ran/TC4 GTPase activating protein, is required for nuclear import
A H Corbett1, D M Koepp, G Schlenstedt
1Division of Cellular and Molecular Biology, Dana Farber Cancer Institute, Boston, MA 02115.
The Journal of Cell Biology
|September 1, 1995
Summary
The Saccharomyces cerevisiae Rna1p protein is crucial for nuclear import. Mutant cells lacking functional Rna1p show defects in protein transport across the nuclear membrane, highlighting its essential role.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- The Saccharomyces cerevisiae gene RNA1 encodes Rna1p, a protein homologous to mammalian Ran/TC4 GTPase activating protein.
- Nuclear import is a fundamental process for eukaryotic cell function, ensuring proteins reach their correct cellular compartments.
Purpose of the Study:
- To investigate the role of Rna1p in protein trafficking across the nuclear membrane.
- To determine if Rna1p directly participates in the nuclear import pathway.
Main Methods:
- Indirect immunofluorescence microscopy to assess nuclear import defects in rna1-1 mutant cells.
- In vitro import assays using fluorescently labeled substrates and semi-intact yeast cells.
- Immunoblotting to confirm Rna1p depletion in mutant extracts.
Main Results:
- Mutant rna1-1 cells exhibited defective nuclear import of several proteins, confirmed by microscopy and green fluorescent protein fusions.
- In vitro assays showed that cytosol from rna1-1 mutants failed to support nuclear import, with extracts depleted of Rna1p.
- Restoration of nuclear import activity was observed upon adding purified Rna1p back to mutant extracts in a dose-dependent manner.
Conclusions:
- Rna1p plays a direct and essential role in the nuclear import of proteins in Saccharomyces cerevisiae.
- The findings establish Rna1p as a key component of the protein trafficking machinery across the nuclear envelope.