exon

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Exon

In split genes, a portion that is included in the ribonucleic acid (RNA) transcript of a gene and survives processing of the RNA in the cell nucleus to become part of a spliced messenger RNA (mRNA) or structural RNA in the cell cytoplasm. Split genes are those in which regions that are represented in mature mRNAs or structural RNAs (exons) are separated by regions that are transcribed along with exons in the primary RNA products of genes, but are removed from within the primary RNA molecule during RNA processing steps (introns). See Intron, Ribonucleic acid (RNA)

Exons comprise three distinct regions of a protein-coding gene. The first is a portion that is not translated into protein, but contains the signal for the beginning of RNA synthesis, and sequences that direct the mRNA to ribosomes for protein synthesis. The second is a set of exons containing information that is translated into the amino acid sequence of a protein. The third region of a gene that becomes part of an mRNA is an untranslated end portion that contains signals for transcription termination and for the addition of a polyadenylate tract at the end of a transcript.

The mechanism by which the exons are joined in RNA copies of genes is called RNA splicing, and it is part of the maturation of mRNAs and some transfer and ribosomal RNAs (tRNAs and rRNAs) from primary transcripts of genes. Three different RNA splicing processes have been identified. One involves mRNA precursors in nuclei, and specific sequences at exon-intron junctions that are recognized by certain nuclear ribonucleoprotein particles that facilitate the cleavage and ligation of RNA. Another applies to nuclear precursors of tRNA, where splice sites are determined by structural features of the folded RNA molecules. The third form of splicing was discovered in studies of protozoan rRNA synthesis, and has also been shown to be a part of the maturation of both rRNA and mRNA in yeast mitochondria; it is an autocatalytic process that requires neither an enzyme nor added energy such as from adenosine triphosphate. See Gene, Genetic code, Protein, Ribosomes

exon

[′ek‚sän]
(genetics)
The segment or segments of a gene which code for its final messenger ribonucleic acid.
References in periodicals archive ?
The effect of an exonic rearrangement on the ORF and possibly the phenotype can be predicted, as the intron-exon boundaries have been well characterised and show that some exons of the DMD gene do not contain an integral number of triplet codons and if deleted will result in a frameshift of the mRNA (Fig.
We have used MLPA for confirming our single exon deletions picked by mPCR, since MLPA probes have exonic ligation sites.
In multiple experiments using a clinically relevant transcriptome discovered by deep sequencing, the research scientists compared the throughput and performance of both profiling technologies and found the new GeneChip([R]) Human Transcriptome and Splice Junction Array outperformed RNA-Seq in most all parameters when detecting exonic changes implicated in human disease and genetic disorders.
Exonic SNPs in the THRSP gene were selected based on the nucleotide sequence of the bovine THRSP gene in GenBank (Accession No.
The 5' proximal end of dystrophin is more susceptible to duplication events and the most common exonic duplication mutation in DMD/ BMD patients has been shown to involve exon 2.
Transcripts were designed to contain the exonic sequences most commonly targeted by BCR-ABL1 RTqPCR assays (Fig.
Resolution is even further enhanced, to the exonic level, in stem cells and cancer related genes.
Of the remaining six polymorphisms, one was an exonic polymorphism (Met287Thr), and five were intronic [C5019T, a 36-bp deletion at 5051, T5194G, a deletion of TTT at 8788, and T12590C].