Single-molecule microscopy reveals that importin α slides along DNA while transporting cargo molecules

Area of Science:

• Molecular Biology
• Cell Biology
• Biophysics

Background:

• Importin α mediates nucleocytoplasmic transport of proteins with nuclear localization signals (NLS).
• Importin α is suggested to directly bind DNA, implying potential roles beyond canonical transport.

Purpose of the Study:

• To investigate the movement dynamics of importin α along DNA.
• To determine if importin α can transport cargo molecules along DNA.
• To explore the role of importin β1/RanGTP in importin α-DNA interactions.

Main Methods:

• Single-molecule fluorescence microscopy.
• Single-tethered DNA arrays.
• Two-color imaging.
• In vivo immunofluorescence assays.

Main Results:

• Importin α exhibits fast and slow diffusion modes along DNA, with fast mode indicating salt-independent sliding.
• Importin α co-slides along DNA with NLS-containing cargo (SV40 TAg-NLS).
• Importin β1/RanGTP enhances importin α DNA binding and cargo recruitment, potentially switching pathways.

Conclusions:

• Importin α actively slides along DNA, demonstrating a novel mechanism for DNA-associated protein dynamics.
• Importin α facilitates efficient cargo transport along DNA, aiding delivery to chromatin regions.
• The importin β1/RanGTP complex may regulate the transition of importin α from nuclear transport to DNA sliding.