An exon is any part of a gene that will encode a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term. Introns are non-coding sections of an RNA transcript, or the DNA encoding it, which are spliced out, or removed, before the RNA molecule is translated into a. In most eukaryotic genes, coding regions (exons) are interrupted by noncoding regions (introns). During transcription, the entire gene is copied into a pre-mRNA, .

Author: Kagajora Nesida
Country: Argentina
Language: English (Spanish)
Genre: Career
Published (Last): 25 July 2010
Pages: 292
PDF File Size: 5.57 Mb
ePub File Size: 12.64 Mb
ISBN: 324-1-72768-459-6
Downloads: 36852
Price: Free* [*Free Regsitration Required]
Uploader: Tojall

Indirect roles of introns Different ordinal position of introns within the gene has a different functional role The first intron among all introns within a gene has particularly been a research focus.

Open in a separate window. For the interferon-based drug used in viral and cancer treatments, see Intron A. Dah and de novo gene birth. Support Center Support Center. When proteins are generated from intron-containing genes, RNA splicing takes place as part of the RNA processing pathway that follows transcription and precedes translation.

Table 1 Summary of direct and indirect intron ejson. Intron size, abundance, and distribution within untranslated regions of genes. Apart from these three short conserved elements, nuclear pre-mRNA intron sequences are highly variable. All eukaryotic genomes carry introns as parts of some gene structures and the introns are to be eliminated by a complex molecular machinery called the spliceosome comprising five snRNAs and more than proteins [ 12 ]. Relationship to nuclear mRNA splicing”.

A survey on intron and exon lengths.

Introns: The Functional Benefits of Introns in Genomes

Molecular biology of the cell. The Evolution of Genome Size. Views Read Edit View history.

Alternative splicing and nonsense-mediated decay modulate expression of important regulatory genes in Arabidopsis. The origin of introns and their role in eukaryogenesis: Exon trapping or ‘ gene trapping ‘ is a molecular biology technique that exploits the existence of the intron-exon splicing to find new genes. Chromatin organization marks exon-intron structure. Majewski J, Ott J. Nonsense-mediated decay NMD was originally lntron as a surveillance mechanism in eukaryotes that selectively removes mRNAs containing erroneously generated premature termination codons PTCs.


In other words, introns may have a role in relaxing intragenic HR interference between sites under the influence of natural selection in finite populations.

Bergman CM, Kreitman M. Besides, introns may give some advantages as a mutational buffer in eukaryotic genomes protecting coding sequences from being affected by randomly occurring deleterious mutations.

The large variation in genome size and C-value across life forms has posed an interesting challenge called the C-value enigma. Fundamentals of Molecular Evolution. Find articles by Bong-Seok Jo.

Many studies have discussed selective advantages that introns bring to the cell in eukaryotes, contributing to overcoming the energetic disadvantage [ 21011121314151617181920 ].

Subsequently, Buchman and Berg [ 48 ] showed that, in a certain condition, constructs with introns were expressed up to times higher than constructs without introns, suggesting that introns can strongly enhance gene expression.

A recent experiment using fluorescence daj situ hybridization has investigated how intron-bearing and ean constructs are distributed differently across the dah and cytoplasm and showed that intron-bearing transcripts are preferentially located in the cytoplasm [ 31 ].

Exon – Wikipedia

Introns certainly impose a huge energetic burden to the cell, considering that the density of introns i. Additionally, several other studies strongly suggesting that introns should not be junk will be introduced. The term exon derives from the expressed region and was coined by American biochemist Walter Gilbert in Introns may be lost or gained over evolutionary time, as shown by many comparative studies of orthologous genes.

The average exon encoded amino acids. The HR interference was basically described as genetic linkage between two sites under selection in finite populations, leading to decreasing effectiveness of natural selection [ 41 ]. These complex architectures allow some group I and group II introns to be self-splicingthat is, the intron-containing RNA molecule can rearrange its own covalent structure so as to precisely remove the intron and link the exons together in the correct order.

In the present review, we first introduce some studies showing what molecular characteristics of introns cannot be explained by a simple random mutational process that real junk DNAs may have undergone.

In tandem genomic duplication, due to the similarity between consensus donor and acceptor splice sites, which both closely resemble AGGT, the tandem genomic duplication of an exonic segment harboring an AGGT sequence generates two potential splice sites. After the initial discovery of introns in protein-coding genes of the eukaryotic nucleus, there was significant debate as to whether introns in modern-day organisms were inherited from a common ancient ancestor termed the introns-early hypothesisor whether they appeared in genes rather recently in the evolutionary process termed the introns-late hypothesis.


Although unicellular eukaryotes such as yeast have either no introns or very few, metazoans and especially vertebrate genomes have a large fraction of non-coding DNA. It is problematic, though, that the ‘function’ of genes in molecular biology generally has been limited in the concept of ‘protein function’.

The frequency of introns within different genomes is observed to vary widely across the spectrum of biological organisms. Different parts of genes have different average sizes of introns, e.

If an allele is significantly more frequent in case groups, the allele is said to be a disease-associated allele, or a trait-associated SNP TAS. We reviewed here putative functional roles of introns in various cellular processes such as splicing, mRNA transport, NMD, and expression regulation.

One of the remarkable examples of the increasing protein repertoire by alternative splicing is the Drosophila Dscam gene, of which over isoforms can potentially be produced by alternative splicing. Fourth, all introns are copied into RNAs by transcription and DNAs by replication processes, but intron sequences do not participate in protein-coding sequences.

For instance, in the human genome only 1. The intron has been a big biological mystery since it was first discovered in several aspects. Robertsfor which they shared the Nobel Prize in Physiology or Medicine in Oswald A, Oates AC. Considering that the ncRNAs located in introns are co-expressed and co-regulated with their host genes by the intronn and splicing machineries of host genes, they are considered to be involved in auto-regulation of the expression of host genes [ 46 ].

In Tetrahymena, the introns located closer to the 5′ end of genes are more conserved than downstream eksonn.