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 ?
In AML, a subset of patients with the t(8;21) translocation and an additional KIT Exon 17 mutation are at increased risk of recurrence compared to those without it, creating a strong need for new therapies to address their form of the disease.
Twenty primer pairs were designed according to the Gallus gallus MRF genes sequences (Table 1) to amplify the eleven exons fully containing the coding sequences of the four genes.
Single exon deletions identified by MLPA were confirmed by standard PCR using primers from the mPCR (if the exon deleted was included in the mPCR multiplexes) or by ordering new primers with alternative primer binding sites.
Figure 1 displays representative difference plots for KRAS exon 2 (Figure 1, A and C) and PIK3CA exon 9 (Figure 1, B and D) from DNA isolated from cell lines (Figure 1, A and B) as well as from DNA isolated from FFPE tissues (Figure 1, C and D).
The diagnosis of B-cell precursor ALL in the presented case warrants comprehensive mutational screening of the entire JAK2 gene coding exon in patients with this type of ALL.
To increase the CFTR mutation detection rate in black and coloured South African CF patients for molecular diagnosis, we tested patients with a clinical phenotype of CF, and at least one unidentified CFTR mutation, for exon CNVs in the CFTR gene: 24 coloured patients (of Khoisan, Malay, European and African admixture), most of whom originate from the Western Cape, and 18 black patients (sub-Saharan African origin) were tested.
For the analysis of the COL4A4 gene, all the exons including splicing sites were amplified by PCR and screened by direct sequencing analysis.
The mutated gene does not allow production of a protein called dystrophin, mainly because of anomalies in the exon which disrupt (or even prevent) its reading.
And, perfectly orchestrated, Wiesener was set to play Exon when the matchups were announced that morning.
Dr Exon added: "It is difficult to know when the surgery could be reopening; we are hoping it is not going to be too much longer.
Luckily, the boundaries between introns and exons are marked.