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

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 ?
Sarepta has another DMD drug in the pipeline, which skips exon 45.
Variants occurring more frequently in exon 11 may be simply explained by the fact that it is the largest exon of the LHCGR gene.
detected GnRHR gene exon 1 in Saanen Dairy Goat and GnRHR gene exon 2 in the Boer goat in the presence of mutation sites, and they were associated with litter size (Han D et al.
KCNE1 has 2-4 exons in several different transcripts in humans, and the last exon is already known to participate in encoding proteins (KCNE1-exon).
One hundred and fifty-four out of 1719 patients did not have any detectable mutation, 39 had rare mutations located in other exons. Remaining 1526 patients (median age 31 [24 to 41] years, 48.4% male) were divided into three subgroups according to the location of the MEFV mutations: Group 1 (exon 2 mutations: E148Q and R202Q), Group 2 (exon 10 mutations: M694V, V726A, M680I, M694I, R761H, K695R), and Group 3 (compound heterozygous; having both exon 2 and exon 10 mutations).
More than 50% of reported mutations have been in exons 3 and 27, the two longest exons of this gene; however, mutational hot-spot sites have not been identified (5).
Primers for coding exon of PAX9 gene were designed by using computer web program Primer3, UCSC genome bio-informatics and ensembl genome browser (table-I).
The anticipated patterns of the 3 enzymes include the cleavage of exon 2 and 3 with BbvI and RsaI, respectively.
Direct sequencing of the genomic PCR products revealed a synonymous mutation, c.657C>T, in exon 3 of NLRP3 that results in the codon substitution ACC to ACT [Figure 1]d; however, this mutation would not cause an amino acid change.
IRESSA (gefitinib) is a targeted monotherapy for the treatment of advanced or metastatic epidermal growth factor receptor (EGFR) exon 19 deletions or exon 21 (L858R) substitution mutation-positive NSCLC.
In the present study, exon 3 was found to be polymorphic at two sites leading to transition at position g A356701G in the coding region and transversion at g G356606T in the third intron of LH[beta] gene as compared to Bubalus bubalis reference sequence.