Intron
Say it: IN-tron
An intron is a stretch of a gene that is copied into RNA but cut out by splicing before the RNA is used, so it does not code for protein.
Also: introns, intervening sequence
Definition
What is an intron?
Introns are noncoding sections that interrupt the coding parts of many eukaryotic genes. When such a gene is transcribed, the first RNA copy, called pre-mRNA, contains both the introns and the exons, the parts that will be kept. Before the RNA leaves the nucleus, a complex called the spliceosome cuts out each intron and joins the exons, so introns are missing from mature messenger RNA and do not specify any amino acids.
Most human protein-coding genes contain introns, and in many genes the introns are far longer than the exons. Nearly all introns in pre-mRNA begin with the bases GU and end with AG, signals that help the spliceosome find where to cut. Introns are not simply wasted space: some contain sequences that control when and how strongly a gene is expressed, and variation in how exons are joined around them lets one gene give several proteins. Mutations that damage a splice site can cause disease.
Introns were discovered in the 1970s, surprising scientists who expected genes to be continuous, as they mostly are in bacteria. Walter Gilbert named them, short for intragenic region.
Word parts
Where does the word “intron” come from?
- intr-
- within, from intragenicLatin intra
- -on
- a unit or regionscientific suffix, as in electron
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Terms that go with it
- ExonAn exon is a section of a gene that stays in the final RNA after splicing removes the introns, and most exons carry code for protein.
- RNA splicingRNA splicing is the step in which introns are cut out of a newly made RNA and its exons are joined, producing a mature RNA ready for use.
- GeneA gene is a stretch of DNA that carries the instructions for making a protein or a working RNA molecule, and is the basic unit of heredity.
- Messenger RNAMessenger RNA is the RNA copy of a gene that carries protein-building instructions from DNA to the ribosomes, where it is read in three-base codons.
- TranscriptionTranscription is the process in which a cell copies the DNA sequence of a gene into a matching strand of RNA.
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