Iwr1 directs RNA polymerase II nuclear import

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• RNA polymerase (Pol) II is essential for transcribing protein-coding genes in eukaryotic cells.
• The precise mechanism of Pol II nuclear import remains largely uncharacterized.
• Pol II is a large complex composed of 12 distinct polypeptide subunits.

Purpose of the Study:

• To elucidate the mechanism of RNA polymerase II nuclear import.
• To identify proteins involved in facilitating the transport of Pol II into the nucleus.
• To investigate the functional cycle of proteins mediating Pol II import.

Main Methods:

• Co-immunoprecipitation assays to detect protein interactions.
• Nuclear localization signal mapping and functional assays.
• Yeast and human cell-based experiments to assess protein function and conservation.

Main Results:

• The protein Iwr1 is identified as a crucial factor for Pol II nuclear import.
• Iwr1 binds to the active center cleft of Pol II, potentially sensing its assembly state.
• Iwr1 utilizes a bipartite nuclear localization signal for karyopherin α-mediated import.
• Iwr1 is displaced by transcription factors and nucleic acids in the nucleus, allowing its recycling.

Conclusions:

• Iwr1 plays a specific and essential role in the nuclear import of RNA polymerase II.
• Iwr1 functions cyclically, binding Pol II in the cytoplasm, facilitating import, and being recycled in the nucleus.
• The function of Iwr1 in Pol II nuclear import is conserved across species, from yeast to humans.