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

exon

[′ek‚sän]
(genetics)
The segment or segments of a gene which code for its final messenger ribonucleic acid.
References in periodicals archive ?
Following conditions were used in thermo cycler for amplification of desired product; First hold, initial denaturation was 95AdegC for 5 min, 25 cycles (denaturation 94AdegC for 30 sec, annealing at 58AdegC for exon 2 and 60AdegC for exon 3 for 30 sec, extension at 72AdegC for 45 sec), final extension 72AdegC for 10 min and finally hold at 4AdegC.
Each of the 13 exons of the PAH gene and its surrounding sequences, an average of 700 bp, were sequenced after amplification and purification.
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.
The TE domain is the part between exons 39 to 41 of the FASN gene (Abe et al.
The researchers also found small exon snippets (micro exons) in fully developed cells.
2]M, a 6 kb gene (357 bp cds), located on 10th chromosome of bovine, is conserved across species, including mammals and birds containing four exons and three introns.
Mutations involve exons 2, 3, 5, 6, 7, 8, 9, 10, 11, 13, 14 of SDHA; exons 1, 2, 3, 4, 6, 7 of SDHB; exons 1, 4, 5 of SDHC; and exons 4 and 6 of SDHD.
Each reported mutation causes skipping of exon 8 at the messenger (mRNA) level, resulting in a frame-shift and produces a prematurely truncated DFNA5 protein.
Hence, we have assessed the levels of clinical severity, biochemical markers, and dystrophin gene deletion pattern in indexed BMD proband by visual examination, fully automated biochemical analyzer, and M-PCR using 26 exons multiplex reaction, respectively.
Some of the most common EGFR tyrosine kinase domain sensitizing and resistance mutations in exons 18-21.
Four primer pairs (Table 1), were designed to amplify exons 1, 2, 3 and 4 of SLA-DRA gene according to the published SLA-DRA gene sequence in GenBank (accession No.