Answer:
The pre-mRNA has to go through some modifications to become a mature mRNA molecule that can leave the nucleus and be translated.
Explanation:
Eukaryotic pre-mRNAs are modified with a 5' methylguanosine cap and a poly-A tail. These structures protect the mature mRNA from degradation and help export it from the nucleus. These include splicing, capping, and addition of a poly-A tail, all of which can potentially be regulated – sped up, slowed down, or altered to result in a different product.
I hope this helps. :).
