An elevated level of the mRNA exporter Mex67-Mtr2 in nuclear mRNPs impairs nuclear mRNA export

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Nuclear mRNA export is vital for gene expression in eukaryotes.
• The Mex67-Mtr2 complex (NXF1-NXT1 in humans) mediates this export.
• Adaptor proteins like Hpr1, Nab2, Yra1, and Npl3 are involved but their roles are not fully understood.

Purpose of the Study:

• To investigate the role of adaptor proteins in mRNA export.
• To determine the effect of Mex67 levels within nuclear mRNPs on export efficiency.
• To elucidate the relationship between Hpr1 function and Mex67 regulation.

Main Methods:

• Analysis of nuclear messenger ribonucleoprotein particles (mRNPs) in Saccharomyces cerevisiae.
• Genetic manipulation including gene deletion (Δhpr1) and overexpression of adaptor proteins (Nab2, Yra1).
• Quantification of Mex67 levels within nuclear mRNPs.

Main Results:

• Cells lacking Hpr1 exhibit impaired nuclear mRNA export with elevated levels of Nab2, Yra1, and Mex67 in nuclear mRNPs.
• Overexpression of Nab2 or Yra1 in Δhpr1 cells rescues the export defect and reduces Mex67 levels in nuclear mRNPs.
• Elevated Mex67 in nuclear mRNPs precedes and likely causes the export defect, not the other way around.

Conclusions:

• Precise regulation of Mex67-Mtr2 levels within nuclear mRNPs is essential for efficient nuclear mRNA export.
• Hpr1 plays a critical role in regulating Mex67 levels, indirectly impacting export.
• Aberrant Mex67 accumulation in mRNPs disrupts the mRNA export pathway.