intron


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Intron

In split genes, a portion that is included in ribonucleic acid (RNA) transcripts but is removed from within a transcript during RNA processing and is rapidly degraded. Split genes are those in which portions appearing in messenger RNAs (mRNAs) or in structural RNAs, termed exons, are not contiguous in a gene but are separated by lengths of deoxyribonucleic acid (DNA) encoding parts of transcripts that do not survive the maturation of RNA (introns). Most genes in eukaryotes, and a few in prokaryotes, are split. These include not just a large number of different protein-coding genes but also genes encoding transfer RNAs (tRNAs) in such diverse eukaryotes as yeast and frogs, and genes encoding structural RNAs of ribosomes in some protozoa. Introns are also found in mitochondrial genes of lower eukaryotes and in some chloroplast genes. See Exon

The number of introns in a gene varies greatly, from 1 in the case of structural RNA genes to more than 50 in collagen. The lengths, locations, and compositions of introns also vary greatly among genes. However, in general, sizes and locations—but not DNA sequence—are comparable in homologous genes in different organisms. The implication is that introns became established in genes early in the evolution of eukaryotes, and while their nucleotide sequence is not very important, their existence, positions, and sizes are significant.

Speculation on the roles and the evolution of introns is mostly based on correlations that have been seen between domains of protein structure and the exons of genes that are defined by intervening introns. For example, the enzyme alcohol dehydrogenase (ADH) has two domains, one portion of the protein that binds alcohol, and another that binds the enzyme cofactor nicotinamide adenine dinucleotide (NAD). The ADH gene has an intron that cleanly separates the nucleotide sequences which encode each domain, and gene-sequence arrangements such as this are not uncommon. It has been suggested that introns became established in the genes of eukaryotes (and to a limited extent in bacteria) because they facilitate a genetic shuffling or rearrangement of portions of genes which encode various units of function, thus creating new genes with new combinations of properties. The introns allow genetic recombination to occur between the coding units rather than within them, thus providing a means of genetic evolution via wholesale reassortments of functional subunits or building blocks, rather than by fortuitous recombinations of actual protein-coding DNA sequences. See Gene, Genetic code, Recombination (genetics)

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

intron

[′in‚trän]
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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BCR 2 Isoform (Variable isoform): Fusion of PML gene involving exon 6 of breakpoint cluster region (bcr) on chromosome 15 with intron 2 of RAR[alpha] gene on chromosome 17 leads to formation of bcr2 (variable isoform) which was detected by conventional double nested PCR.
According to the terms of the contract, iNtRON Bio will receive an upfront payment upon execution of the contract and subsequent milestone payments for development, regulatory, and sales-driven events.
As far as intron 9 is concerned, insertion of (T) and (C) were observed in all cases and control instead of reference sequence of two positions 11696, 11698, while one sample (DP26) was heterozygous (G/C) at position 12399 in intron 10 instead of homozygous (G) in all other cases including normal and reference controls (Table 4, Figure 2b)
In this study, the genetic analysis were performed to identify the polymorphic sites of (C1071T), (G1072A), (T1081C), (T1131G), (T1143C), (T1145G), (T1151G) and (C1221T) (GenBank) of (containing the exon 2, part of the intron 1 and intron 2) bubaline leptin gene in Anatolian water buffaloes.
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The remainder of 22 distinct mutations was detected once in heterozygosity each accounting for 0.8% (n =118) (Supplementary Table 2, Table 1), including five of the six previously unreported potentially pathogenic mutations p.Trp12* (exon 1), p.Asn76Thr (exon 3), p.Ser673Argfs*6 (exon 14), p.Cys698Arg (exon 14), and c.4352+4A>C (intron 29).
In conclusion, we suggested that the intron 3 VNTR variant in the XRCC4 gene may be associated with the etiopathogenesis of RA as a marker of immune aging.
The PPAR[alpha] G2467C intron 7 polymorphism (rs 4253778) was studied by PCR-RFLP technique, using a 5' forward primer of ACA ATC ACT CCT TAA ATA TGG TGG and a 3' reverse primer of AAG TAG GGA CAG ACA GGA CCA GTA.
The sequencing data showed that AT1 and AT2 had an extended form of exon 8 and that AT3 had an extended exon 8 that included about 25 bp of intron 8 (Figure 3).
Name Forward Reverse 1 GTC TCA CAA CTC GCG TCC G GCC TGA AAT GGA GGG AAA GCA 2 TCG AGA TCC TGG ACC GGT AA GGC CAC ATT TTT GCA GCC TAA 3 GCA GCT ATT GAT GTG CGT CC TGA AGG GAG ACA GCT CTT GTG 4 ACT CAG CCA ACC TGA TTT CCT AC TTC AGA GCC CAG GAG TCA GT Name Products 1 Exon 1 and boundaries 2 Exons 2, 3 and intron 2; boundaries 3 Exons 4, 5, 6 and introns 4, 5; boundaries 4 Exons 7, 8 and intron 7; boundaries TABLE 3: Statistics of minor allele frequency (MAF).
Some meta-analyses have shown the association between the NOS3 polymorphisms and hypertension, highlighting the intron 4b/a and 894G>T polymorphisms [20-22].
Fifth, they primarily come from exons, while a few others come from introns or intron fragments.