Gene expression
4. Maturation of the eukaryotic pre-mRNA transcript
4.3 Intron splicing
Primary transcripts of mRNA consist of alternating introns and exons.
Intron: Sequence removed during maturation of mRNA and not present in final mRNA. Introns are often between 100 and 5000 nucleotides in length (up to 100,000 nucleotides).
Exon: A non-eliminated sequence, thus present in the final mRNA. Exons are often between 100 and 200 nucleotides in length.
During maturation of eukaryotic mRNA, introns are eliminated through a mechanism termed splicing.