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Monday 7 January 2008

An exon is any region of DNA within a gene that is transcribed to the final messenger RNA (mRNA) molecule, rather than being spliced out from the transcribed RNA molecule. Exons of many eukaryotic genes interleave with segments of non-coding DNA (introns). The term exon was coined by American biochemist Walter Gilbert in 1978. (WP)

In many genes, each exon contains part of the open reading frame (ORF) that codes for a specific portion of the complete protein. However, the term exon is often misused to refer only to coding sequences for the final protein. This is incorrect, since many noncoding exons are known in human genes.

Some of the exons will be wholly or part of the 5’ untranslated region (5’ UTR) or the 3’ untranslated region (3’ UTR) of each transcript. The untranslated regions are important for efficient translation of the transcript and for controlling the rate of translation and half life of the transcript. Furthermore, transcripts made from the same gene may not have the same exon structure since parts of the mRNA could be removed by the process of alternative splicing. Some mRNA transcripts have exons with no ORF’s and thus are sometimes referred to as non-coding RNA.

Exonization is the creation of a new exon, as result of mutations in intronic sequences.

Polycistronic messages have multiple ORF’s in one transcript and also have small regions of untranslated sequence between each ORF.

New exons

The origin of new exons is an important mechanism for proteome diversity.

See also

- exon trapping


- Li X, Liang J, Yu H, Su B, Xiao C, Shang Y, Wang W. Functional consequences of new exon acquisition in mammalian chromodomain Y-like (CDYL) genes. Trends Genet. 2007 Sep;23(9):427-31. PMID: 17573145