Yeast nucleoporins involved in passive nuclear envelope permeability

Area of Science:

• Cell Biology
• Molecular Biology
• Biophysics

Background:

• The nuclear pore complex (NPC) is a large protein structure that controls the transport of molecules between the nucleus and cytoplasm.
• The NPC contains a central channel with a specific diameter that limits the passive diffusion of molecules.
• Understanding the regulation of NPC channel size is crucial for comprehending nucleocytoplasmic transport dynamics.

Purpose of the Study:

• To investigate the role of specific nucleoporins (Nup170p and Nup188p) in regulating the permeability of the nuclear envelope (NE).
• To determine how mutations in NUP188 and NUP170 affect the transport of molecules through the NPC.
• To explore the specificity of heat shock protein 70 (Hsp70) in nuclear import pathways.

Main Methods:

• Utilized Saccharomyces cerevisiae (yeast) as a model organism.
• Employed green fluorescent protein (GFP) reporters fused with nuclear localization signals (NLS) and nuclear export signals (NES).
• Assessed passive transport rates and equilibrium sieving limits in wild-type and mutant yeast strains (nup188-Delta, nup170-Delta).

Main Results:

• Deletion mutants of Nup188p (nup188-Delta) and Nup170p (nup170-Delta) exhibited significantly faster passive export rates.
• These mutants also showed increased equilibrium sieving limits for molecules up to 126 kD.
• Heat shock protein 70 (Hsp70) stimulation enhanced the import of one NLS-GFP reporter but not another, indicating pathway specificity.

Conclusions:

• Nup170p and Nup188p are key components in establishing the resting diameter of the NPC's central transport channel.
• The findings suggest that Nup170p and Nup188p play a critical role in maintaining the size-selective barrier of the nuclear envelope.
• The study highlights the NLS- and targeting pathway-specific function of Hsp70 in nuclear import.