Nuclear Export of mRNA

For protein synthesis, the mature mRNA needs to be transported from the nucleus to the cytoplasm.

Embedded throughout the nuclear membrane are large protein complexes known as nuclear pore complexes or NPCs. These function as selective channels between the nucleus and cytoplasm, only allowing some macromolecules to pass through.

An NPC has a hollow, cylindrical structure composed of a class of proteins called nucleoporins, which has about 30 distinct members. 

To pass through the NPC, the mRNA associates with another protein called a nuclear transport receptor. They form an RNA- receptor complex that can now be shuttled through the NPC channel into the cytoplasm, followed by dissociation of the complex. 

Now, the receptor can return to the nucleus to transport another mRNA.

The mature mRNAs are a small fraction of the RNA species present in a cell. The remainder consists of junk RNAs, such as pre-spliced mRNA, excised introns, and incompletely or irregularly spliced products.

During transcription and post-transcriptional processing, a regular mRNA with a 5’ cap and a 3’ poly A tail, associates with various proteins such as-Cap binding complex or CBC, Exon junction complex or EJC, P