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 ?
All mutations were correctly retrieved, apart from the 2 exonic deletions (deletion of exons 7-8 in 1 patient and exons 7-10 in the other sample).
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.
Walter and colleagues spied on the splicing process by attaching fluorescent tags to exons on either side of an intron in a short section of RNA they designed specifically for such studies.
A heterozygous deletion of exon 2 was detected in a single black CF patient, using both MLPA and semi-quantitative fluorescent PCR.
Amplification of exons of the COL4A4 gene: Genomic DNA was obtained from the peripheral blood lymphocytes using FlexiGene DNA kit (QIAGEN Hilden, Germany).
In targeting just 6 exons, this technique could affect 85% of dystrophin gene deletions in human (database: JC Kaplan, Cochin Institute).
After heating 20% buffered formalin-fixed and paraffin-embedded histologic sections at 96 [degrees] C for 20 minutes for antigen retrieval, PCR products for K-ras gene exons 1 and 2, and p53 exons 5 through 9 could be generated from recovered solutions in all 20 cases of colorectal carcinoma.
Like its other microarrays, Agilent also provides custom options for the human, mouse and rat SurePrint G3 Exon products.
There are currently four companies around the world focused on developing exon-skipping strategies for Duchenne, with antisense oligonucleotides targeting exons 51, 44, 45 and 53 in clinical testing now.
With the exception of exon 7 and exon 9, all other exons very short.
For all of the other selected genes, we designed partially overlapping probes (15 bp as the maximum-acceptable overlap) that covered only all of the exons and the 5' and 3' untranslated regions (see Fig.
This whole process should start with computational approach, first in characterization of genes in a particular species of importance and looking at homologous DNA sequences that are conserved across different taxa, followed by comparison of length of genes and introns and exons (in nucleotides), number of introns and exons, distribution of CpG islands, etc.