An intron is a non-coding sequence in a gene.
It is any nucleotide sequence within a gene that is removed by RNA splicing to get the final RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts.
Introns are in the genes of most organisms and many viruses. They can be in a wide range of genes, including those that generate proteins, ribosomal RNA (rRNA), and transfer RNA (tRNA). RNA splicing takes place after transcription and before translation.
- Introns: parts of a gene which are discarded: non-working bits.
- Exons: parts of a gene which are expressed: bits of a gene which code for amino-acid sequences in a protein.
Biological meaning[change | change source]
Recent studies of entire eukaryotic genomes have now shown that the lengths and density (introns/gene) of introns varies considerably between related species. There are four or five different kinds of intron. Some introns represent mobile genetic elements (transposons).
Alternative splicing of introns within a gene allows a variety of protein isoforms from a single gene. Thus multiple related proteins can be generated from a single gene and a single precursor mRNA transcript. The control of alternative RNA splicing is performed by complex network of signalling molecules. In humans, ~95% of genes with more than one exon are alternatively spliced.
References[change | change source]
- Alberts, Bruce (2008). Molecular biology of the cell. New York: Garland Science. .
- Stryer, Lubert; Berg, Jeremy Mark; Tymoczko, John L. (2007). Biochemistry. San Francisco: W.H. Freeman. .
- Kinniburgh, Alan; Mertz J. and Ross J. (July 1978). "the Precursor of mouse β-globin messenger RNA contains two intervening RNA sequences". Cell 14 (3): 681-693. http://www.cell.com/abstract/0092-8674(78)90251-9#.
- Gilbert, Walter (1978). "Why genes in pieces". Nature 271 (5645): 501. . .
- Orgel L.E. & Crick, F.H.C. 1980. Selfish DNA: the ultimate parasite. Nature, 284, 604-607.
- Pan, Q; Shai O, Lee LJ, Frey BJ, Blencowe BJ 2008. Deep surveying of alternative splicing complexity in the human transcriptome by high-throughput sequencing. Nature Genetics 40 (12): 1413–1415. doi:10.1038/ng.259. PMID 18978789.