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Ran-dependent signal-mediated nuclear import does not require GTP hydrolysis by Ran
E D Schwoebel1, B Talcott, I Cushman
1Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
The Journal of Biological Chemistry
|December 18, 1998
Summary
Nuclear import does not require nucleotide hydrolysis for protein transport. A pool of GTP is necessary, and GTP hydrolysis is restored by adding RCC1, the Ran guanine nucleotide exchange factor.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Nuclear import of proteins is crucial for cellular function.
- This process was traditionally believed to require nucleotide hydrolysis for energy.
Purpose of the Study:
- To investigate the necessity of GTP hydrolysis in the nuclear import of classical nuclear localization sequence-containing proteins.
Main Methods:
- Utilized hydrolysis-resistant GTP analogs.
- Employed a mutant Ran protein deficient in GTP hydrolysis.
- Assessed nuclear import and substrate release in vitro.
Main Results:
- Nuclear import and substrate release into the nucleus did not require GTP hydrolysis by Ran.
- No requirement for hydrolysis of any nucleotide triphosphate was observed for this import process.
- A pool of free GTP was found to be necessary, likely for converting GDP-bound Ran to GTP-bound Ran.
- GTP hydrolysis requirement was restored by adding RCC1 (Ran guanine nucleotide exchange factor).
Conclusions:
- GTP hydrolysis is not essential for the movement and release of classical nuclear localization sequence-containing proteins through the nuclear pore complex.
- The availability of free GTP is critical for maintaining the RanGTP/RanGDP ratio necessary for import.
- RCC1 plays a key role in restoring the GTP hydrolysis requirement in reconstituted systems.