mRNAexport

mRNA export is the cellular process by which mature messenger RNA is transported from the nucleus to the cytoplasm for translation. In eukaryotic cells, transcription, capping, splicing, and 3’ end processing occur before export, and only properly processed mRNAs are shuttled through the nuclear pore complexes (NPCs) to reach the cytoplasm.

The export of mRNA relies on conserved molecular machines. The major export receptor in metazoans is the heterodimer NXF1-NXT1 (also known as TAP-p15), which binds mRNPs and interacts with FG-repeat nucleoporins during transit through the NPC. In yeast, Mex67-Mtr2 serves a similar function. The mRNP is prepared for export by the TREX complex, which couples transcription to export; TREX includes the THO complex and the DEAD-box helicase Sub2/UAP56, with Aly/REF (Yra1 in yeast) helping recruit the export receptor to the mRNP. Splicing and other processing events can enhance export efficiency by promoting TREX association.

Passage through the NPC involves docking with nucleoporins and guided transit by the export receptor. On the cytoplasmic side, ATP-dependent remodeling by the helicase Dbp5 (Ddx19 in humans), with Gle1 and inositol hexakisphosphate, remodels the mRNP and releases export factors to permit translation initiation.

Quality control ensures only properly processed mRNAs are exported; aberrant transcripts may be retained or degraded. Export is regulated during development and stress, and defects in export factors can cause nuclear retention, altered gene expression, or disease. Yeast and metazoans share core principles, though higher eukaryotes feature additional regulatory layers and variants of the export machinery.