Answer:
removal of introns, addition of 5' cap and 3' tail to mRNA.
Explanation:
The mRNA is processed before it leaves nucleus. The introns are removed and exons are remain in mRNA. This process is called splicing. The 5' end is attached with a cap and 3' is attached with a polyadenylated tail. Thus mRNA is processed with these process before it leaves the nucleus.
