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Intron

(Science: molecular biology) a noncoding sequence of dna within a gene, that is transcribed into hnrna but is then cut out of the message by rna splicing in the nucleus, leaving a mature mrna that is then translated in the cytoplasm.

introns are poorly conserved and of variable length, but the regions at the ends are self complementary, allowing a hairpin structure to form naturally in the hnrna, this is the cue for removal by rna splicing. Introns are thought to play an important role in allowing rapid evolution of proteins by exon shuffling. Genes may contain as many as 80 introns.

Compare: exon