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Sequence and characterization of cytoplasmic nuclear protein import factor p97
1Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
The Journal of Cell Biology
|July 1, 1995
Summary
Nuclear protein import involves karyophile binding to nuclear pore complexes. The protein p97 is crucial for this process, interacting with other cytosolic factors and requiring zinc for nuclear envelope binding.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Nuclear protein import is essential for cellular function.
- The initial step involves karyophile binding to nuclear pore complexes.
- Two key cytosolic proteins, NLS receptor and p97, were previously identified.
Purpose of the Study:
- To further characterize the role of p97 in nuclear protein import.
- To investigate the interaction of p97 with other cellular components.
- To determine the structural and functional requirements for p97 activity.
Main Methods:
- Immunolocalization using a monoclonal antibody against p97.
- Extraction of p97 from nuclear envelopes.
- Permeabilized cell import assays.
- Immunodepletion of p97 from cytosol.
- cDNA cloning and recombinant protein expression.
- Zinc binding assays.
Main Results:
- p97 localizes to the cytoplasm and nuclear envelope, tightly associated with nuclear pore complexes.
- Antibody against p97 inhibits import but not karyophile binding.
- p97 depletion inactivates cytosol for import and reveals interactions with other proteins.
- Recombinant p97 binds zinc, and this metal ion is necessary for nuclear envelope binding.
Conclusions:
- p97 is a critical cytosolic factor for nuclear protein import, acting downstream of initial karyophile binding.
- p97's interaction with the nuclear pore complex and its zinc-binding capability are essential for its function.