Structural basis for polyadenosine-RNA binding by Nab2 Zn fingers and its function in mRNA nuclear export

Area of Science:

• Molecular Biology
• RNA Biology
• Protein Structure

Background:

• Nab2 is crucial for polyadenylation and mRNA export.
• It contains seven CCCH zinc fingers involved in RNA binding.
• Efficient nuclear export of messenger ribonucleoprotein particles (mRNPs) is vital for gene expression.

Purpose of the Study:

• To determine the solution structure of Nab2's C-terminal zinc fingers (5-7).
• To investigate the role of these fingers in polyadenosine-RNA binding and mRNP export.
• To elucidate the relationship between Nab2, Dbp5, and Yra1 in RNA processing and export.

Main Methods:

• Solution structure determination of Nab2 zinc fingers 5-7.
• Site-directed mutagenesis to create Nab2 variants (e.g., Nab2-C437S).
• Analysis of genetic interactions and suppression of mutant alleles (rat8-2, Yra1).

Main Results:

• Nab2 fingers 5-7 form a single structural unit essential for high-affinity polyadenosine-RNA binding.
• A Nab2 mutant (C437S) with compromised RNA binding suppresses the Dbp5 (rat8-2) mutation.
• Suppression is linked to hyperadenylation and Yra1 function, not directly to RNA binding affinity.

Conclusions:

• Nab2 plays an unexpected role in generating export-competent mRNPs beyond poly(A) tail length regulation.
• Structural alterations in Nab2 fingers 5-7 can lead to suboptimal mRNP assembly.
• These defects make mRNP export complexes more susceptible to disassembly by Dbp5 in the cytoplasm.