exon Part of the DNA of a gene that encodes the information for the amino-acid sequence in a polypeptide. Many eukaryote genes contain a series of exons alternating with introns; following transcription, the introns are excised and the exon sequences are joined together to form m-RNA, which is used in protein synthesis.

exon A nucleotide sequence in a gene that codes for part or all of the gene product and is therefore expressed in mature messenger RNA, ribosomal RNA, or transfer RNA. In eukaryotes, exons are separated by noncoding sequences called introns.

exon That part of a gene which appears in the mature RNA transcript.