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Nuclear import of the stem-loop binding protein and localization during the cell cycle
Judith A Erkmann1, Eric J Wagner, Jian Dong
1Program in Molecular Biology and Biotechnology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
Molecular Biology of the Cell
|April 15, 2005
Summary
Stem-loop binding protein (SLBP) shuttles between the nucleus and cytoplasm during the cell cycle, dependent on histone mRNA binding. Nuclear import is mediated solely by the Impalpha/Impbeta pathway.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Stem-loop binding protein (SLBP) is crucial for histone mRNA processing and translation.
- Understanding SLBP's dynamic localization is key to regulating gene expression.
Purpose of the Study:
- To investigate the nuclear transport and cell cycle-dependent subcellular localization of SLBP.
- To elucidate the mechanisms governing SLBP's import and export pathways.
Main Methods:
- Cell cycle analysis of SLBP localization using microscopy.
- Heterokaryon assays to study nuclear export.
- In vitro import assays with purified SLBP and import receptors.
- Site-directed mutagenesis to identify SLBP nuclear localization signals.
Main Results:
- SLBP is predominantly nuclear but translocates to the cytoplasm during S phase.
- SLBP nuclear export requires histone mRNA binding; SLBP lacks intrinsic export signals.
- SLBP interacts with importin-alpha/beta (Impalpha/Impbeta) and Transportin-SR2.
- RanGTP disrupts SLBP-importin complexes.
- SLBP is imported by both Impalpha/Impbeta and Transportin-SR2 in vitro.
- Three specific sequences in SLBP are essential for Impalpha/Impbeta binding and nuclear import in vivo.
Conclusions:
- SLBP nuclear import in HeLa cells relies exclusively on the Impalpha/Impbeta pathway.
- Histone mRNA binding dictates SLBP's nuclear export, linking its localization to its function.