What types of modifications may occur to a molecule of messenger RNA before it leaves the nucleus?

RNA processing occurs on a primary mRNA transcript before it leaves the nucleus. This involves:





1. 5' capping - a modified G nuelotide is added to the 5' end;





2. addition of the poly-A tail at the 3' end (about 200 adenine residues);





3. and splicing, during which intron sequences are removed and exons "glued" together.