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Updated: Jul 6, 2026
12:13
Single-Molecule Imaging of Nuclear Transport
Published on: June 9, 2010
Nopp140 shuttles on tracks between nucleolus and cytoplasm
1Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York, New York 10021.
Cell
|July 10, 1992
Summary
Nopp140, a nucleolar phosphoprotein, binds nuclear localization signals (NLS) in a phosphorylation-dependent manner. It shuttles between the nucleolus and cytoplasm, potentially acting as a chaperone for nucleolar transport.
Area of Science:
- Cell Biology
- Molecular Biology
- Protein Biochemistry
Background:
- Nopp140 is a 140 kDa nucleolar phosphoprotein.
- It was initially identified as a nuclear localization signal (NLS)-binding protein.
Purpose of the Study:
- To characterize the molecular properties of Nopp140.
- To investigate the role of phosphorylation in NLS binding.
- To elucidate the transport pathway and function of Nopp140.
Main Methods:
- Protein purification and characterization.
- Analysis of phosphorylation sites for casein kinase II (CK II).
- Immunoelectron microscopy to visualize transport tracks.
Main Results:
- Nopp140 contains a 10-fold repeated acidic serine cluster motif with abundant CK II phosphorylation sites.
- Nopp140 is highly phosphorylated, and NLS binding is phosphorylation-dependent.
- Nopp140 shuttles between the nucleolus and cytoplasm via tracks extending to nuclear pore complexes.
Conclusions:
- Nopp140 functions as a nucleolar phosphoprotein with phosphorylation-dependent NLS binding.
- It utilizes specific tracks for nucleocytoplasmic shuttling.
- Nopp140 is proposed to act as a chaperone for nucleolar import and/or export.
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