Exon

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The exon portion of a DNA strand encodes a specific portion of a . In some organisms exons are situated between  which are spliced from the strand before it is exported from the nucleus and do not code for protein parts.
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The exon portion of a DNA strand encodes a specific portion of a protein. In some organisms exons are situated between introns which are spliced from the strand before it is exported from the nucleus and do not code for protein parts.
Missing image
Exon-intron.jpg
Simple illustration of exons and introns.

Exons are the regions of DNA within a gene that are not spliced out and which are retained in the final mRNA molecule.

In many genes, each exon contains part of the open reading frame (ORF) that codes for a specific portion of the complete protein, however, not all exons in a given gene will code for the final protein. Some of the exons will be mRNA that is 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 as well as being important 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.

Exon trapping or 'gene trapping' is a molecular biology technique that exploits the existence of the intron-exon splicing to find new genes. The first exon of a 'trapped' gene will splice into the exon that is contained in the insertional DNA. This new exon contains the ORF for a reporter gene that can now be expressed using the enhancers that control the target gene. A scientist knows that a new gene has been trapped when the marker gene is expressed.

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

Splicing can be experimentally modified so that targeted exons are excluded from mature mRNA transcripts by blocking the access of splice-directing proteins to pre-mRNA using Morpholino antisense oligos. This has become a standard technique in developmental biology.

See also

External links and references

es:exón he:אקסון_(גנטיקה) ja:エクソン

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