Introns are areas of DNA that must be discarded from the primary RNA transcript. The most common are of the eukaryotic RNA class, mainly in messenger RNAs, in the same way they can be located in certain prokaryotic rRNAs and tRNAs. The quantity and dimension of introns is very diverse between species. They were first discovered by chemists Phillips Allen Sharp and Richard J. Roberts.
The research carried out by these specialists on introns made them worthy of the Nobel Prize in physiology and medicine. However, the term “intron” was brought to light by the biochemist Walter Gilbert, in 1978.
Introns can represent an optional area of "splicing" better known as " splicing ", being able to originate different forms of proteins. The splicing process will be controlled by a wide variety of molecular signals. Another interesting fact is that introns can also include old data, that is, they can contain parts of genes that could have been expressed previously, but currently do not.
Classical theories have affirmed that introns are pieces of DNA that do not have information, although this information is in debate and nowadays it does not have many supporters.
Introns are classified into:
- Class I introns.
- Class II introns.
- Class III introns.
- Class IV introns.
Class I and II introns tend to suffer from spliceosomes (splicing complex) through transesterification reactions. The times it is possible to find this group of introns in the genome, it is relatively rare. Class II and III introns are very similar and have a highly conserved secondary system. Class IV introns are found in eukaryotic tRNAs and are distinguished by being the only ones that are shed through an endonucleotide cut.
Introns can be found frequently in multicellular eukaryotes, such as humans, and less frequently in single-celled eukaryotes, such as yeast. In the case of archeas and bacteria they are rare.
