A portion of DNA that lies between two exons, is transcribed into RNA, but does not appear in that mRNA after maturation because the intron is removed and the exons spliced together, and so is not expressed (as protein) in protein synthesis. By customary usage, the term is extended to the corresponding regions in the primary transcript of mRNA before maturation.
Synonym(s): intervening sequence
[inter- + -on]
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Examples: glitazone, GI cocktail, etc.