Answer :
Splicing, adding of the cap and tail, and the exit of the mRNA from the nucleus.
The three major steps in mRNA processing are capping, splicing and polyadenylation.
What is mRNA processing?
The mRNA produced by the process of transcription of DNA is not functional and needs further processing. This mRNA is called precursor mRNA or pre mRNA.
The result of the processing is the production of mature mRNA which can be translated to form proteins.
mRNA modifications required to yield mature mRNA are 5' capping, splicing of introns, and 3' polyadenylation.
5' capping means the addition of a 7' methylguanosine cap (m7g) to the 5' end of the mRNA.
Introns are non-coding regions present in the precursor mRNA which need to be removed. These are removed by the process of mRNA splicing. The coding regions are called exons which are joined after the introns are removed. Exons can be translated into proteins.
At the 3' end of the pre mRNA, cleavage occurs and 250 adenine residues are added. This forms a polyadenylated tail at the 3' end of the mRNA.
Therefore the three major steps in mRNA processing are capping, splicing and polyadenylation.
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