The nuclear export receptor Xpo1p forms distinct complexes with NES transport substrates and the yeast Ran binding...

Area of Science:

• Cell Biology
• Molecular Biology
• Protein Transport

Background:

• Xpo1p (Crm1p) is the primary nuclear export receptor for proteins with leucine-rich nuclear export signals (NES).
• Nuclear export involves the formation of a complex between Xpo1p, the cargo protein, and GTP-bound Ran (Gsp1p in yeast).

Purpose of the Study:

• To identify proteins that bind to Xpo1p in the presence of GTP-bound Gsp1p in Saccharomyces cerevisiae.
• To characterize the interaction between Yrb1p and the Xpo1p-Gsp1p-GTP complex and its role in nuclear export.

Main Methods:

• Biochemical assays using yeast extracts to identify Xpo1p-binding proteins.
• Analysis of protein localization and shuttling dynamics.
• Characterization of protein-protein interactions and complex formation.

Main Results:

• Yrb1p was identified as a major binding partner of Xpo1p in the presence of Gsp1p-GTP.
• Yrb1p, a shuttling protein, interacts with Xpo1p-Gsp1p-GTP independently of a classical NES.
• This interaction requires the acidic C-terminus of Gsp1p and is distinct from importin beta-like receptor binding.
• Yrb1p acts as a disassembly factor for NES-containing complexes and facilitates their dissociation after GTP hydrolysis by Rna1p.

Conclusions:

• Yrb1p mediates a novel pathway for nuclear export involving Xpo1p and Gsp1p-GTP.
• Yrb1p plays a crucial role in regulating nuclear transport by both facilitating export and promoting complex disassembly.
• The findings reveal a new mechanism for controlling protein trafficking through the nuclear pore.