exon

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Related to Exons: RNA splicing

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

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

exon

[′ek‚sän]
(genetics)
The segment or segments of a gene which code for its final messenger ribonucleic acid.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Indeed, our previous meta-analysis demonstrated that, among all genotypes, GIST patients with the KIT exon 11 mutation were the most sensitive to imatinib [8].
Of 160 mutation cases, the most common mutation was an in-frame deletion in exon 19, comprising 48.8% (78/160) of all mutations found, followed by a point mutation (L858R) in exon 21, comprising 36.9% (59/162) of mutations.
Each of the 13 exons of the PAH gene and its surrounding sequences, an average of 700 bp, were sequenced after amplification and purification.
Williamson et al suggested that PCR-based screening analysis of exon 3 and exon 4 is the first step for genetic diagnosis of RTT because of the majority of mutations are seen in these regions.
(4) The BDNF gene in the rat contains eight 5' noncoding exons (I-IXa), each with a separate promoter and one 3' coding exon (IX) that comprises the entire open reading frame for BDNF protein.
Various coding silent substitutions (nucleotide change without amino acid change in the EGFR protein) were observed, mainly in exons 20 and 21 (Table 2).
We use the HEXEvent database, which provides a list of human internal exons and reports all known splice events, as our source of alternative splicing information [17].
(a) Examples of normal and patient dystrophin gene exons. Individual exons are represented by beige, dark blue, light blue, and brown.
Various studies have reported coding missense mutation in exon 3 of NURR1 (709C>G and 711 C/A), -291Tdel and -245T[right arrow]G sequence variation in the noncoding exon-1 within the 5' untranslated region, and mutations in exon 2 at 388 G/A, 35 A/G, and 21 C/G respectively, including some intron regions which markedly attenuates NURR1-induced transcriptional activation, leading to decreased expression being identified in a patient with PD [14, 34].
Of the two variants, one is a novel missense variant in exon 4 (c.349G>A, p.Gly117Arg), and the other was a novel nonsense variant in exon 10 (c.878C>A, p.Ser293 *).
Conclusion: In summary, this study showed two SNP loci that were found in the GnRHR gene exons 1 and exon 2 of the giant panda.
Of the three exons, only KCNE3-exon-3 had four mutation loci (Table 2), and only KCNE3-exon-3 is known to participate in encoding proteins.