Prototype of mature eukaryotic mRNA

Mature eukaryotic mRNA is produced from its
precursor RNA by the removal of introns, addition
of a 5! cap at the 5! end, and addition of
numerous adenine nucleotides at the 3! end
(polyadenylation). A noncoding sequence (5!
leader) is located in front of the translation start
signal (AUG), and a trailer sequence, at the 3!
end in back of the translation stop signal (UAA).
Both addition of the 5! cap and polyadenylation
involve enzymatic reactions.