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Simple illustration of an unspliced mRNA precursor, with two introns and three exons (top). After the introns have been removed via splicing, the mature mRNA sequence is ready for translation (bottom). A particularly extreme case is the Drosophila dhc7 gene containing a ≥3.6 megabase (Mb) intron, which takes roughly three days to transcribe.
Some non-coding RNA transcripts also have exons and introns. Mature mRNAs originating from the same gene need not include the same exons, since different introns in the pre-mRNA can be removed by the process of alternative splicing. Exonization is the creation of a new exon, as a result of mutations in introns. [12]
When the pre-mRNA has been transcribed from the DNA, it includes several introns and exons. (In nematodes, the mean is 4–5 exons and introns; in the fruit fly Drosophila there can be more than 100 introns and exons in one transcribed pre-mRNA.) The exons to be retained in the mRNA are determined during the splicing process. The regulation and ...
The split gene theory is a theory of the origin of introns, long non-coding sequences in eukaryotic genes between the exons. [1] [2] [3] The theory holds that the randomness of primordial DNA sequences would only permit small (< 600bp) open reading frames (ORFs), and that important intron structures and regulatory sequences are derived from stop codons.
RNA splicing is a process in molecular biology where a newly-made precursor messenger RNA (pre-mRNA) transcript is transformed into a mature messenger RNA ().It works by removing all the introns (non-coding regions of RNA) and splicing back together exons (coding regions).
The RNA that results from RNA splicing is a sequence of exons. The reason why introns are not considered untranslated regions is that the introns are spliced out in the process of RNA splicing. The introns are not included in the mature mRNA molecule that will undergo translation and are thus considered non-protein-coding RNA.
Pre-mRNA has both introns and exons. As a part of the maturation process, RNA splicing removes the non-coding RNA introns leaving behind the exons, which are then spliced and joined together to form the mature mRNA. [3] [8] Splicing is conducted by the spliceosome. The spliceosome is a large ribonucleoprotein which cleaves the RNA at the ...
In eukaryotic genes with multiple exons, introns are removed and exons are then joined together after transcription to yield the final mRNA for protein translation. In the context of gene finding , the start-stop definition of an ORF therefore only applies to spliced mRNAs , not genomic DNA, since introns may contain stop codons and/or cause ...