Mature messenger RNA

Mature messenger RNA, often abbreviated as mature mRNA is a eukaryotic RNA transcript that has been spliced and processed and is ready for translation in the course of protein synthesis. Unlike the eukaryotic RNA immediately after transcription known as precursor messenger RNA, ^[1] mature mRNA consists exclusively of exons and has all introns removed.

The Maturation of mRNA

Mature mRNA is also called "mature transcript", "mature RNA" or "mRNA".

The production of a mature mRNA molecule occurs in 3 steps: ^{[2] [3]}

1. Capping of the 5' end
2. Polyadenylation of the 3' end
3. RNA Splicing of the introns

Capping the 5' End

During capping, a 7-methylguanosine residue is attached to the 5'-terminal end of the primary transcripts.This is otherwise known as the GTP or 5' cap. The 5' cap is used to increase mRNA stability. Further, the 5' cap is used as an attachment point for ribosomes. ^[1] Beyond this, the 5' cap has also been shown to have a role in exporting the mature mRNA from the nucleus and into the cytoplasm. ^[4]

Polyadenylation

In polyadenylation, a poly-adenosine tail of about 200 adenylate residues is added by a nuclear polymerase post-transcriptionally. This is known as a Poly-A tail and is used for stability and guidance, so that the mRNA can exit the nucleus and find the ribosome. ^[5] It is added at a polyadenylation site in the 3' untranslated region of the mRNA, cleaving the mRNA in the process. ^[6] When there are multiple polyadenylation sites on the same mRNA molecule, alternative polyadenylation can occur. ^[7] See polyadenylation for further details.

RNA Splicing

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 splicing site and recombines the exons of the RNA. Similar to polyadenylation, alternative splicing can occur, resulting in several possible proteins being translated from the same portion of DNA. ^[9] See RNA Splicing for further details.

References

1. Alberts, Bruce (2015). Molecular biology of the cell (Sixth ed.). Abingdon, UK: Garland Science, Taylor and Francis Group. ISBN   978-0815344643.
2. O'Connor, Clare (2010). Essentials of Cell Biology. NPG Education: Cambridge, MA. Retrieved November 11, 2021.
3. Toole, Glenn; Toole, Susan (2015). AQA biology A level. Student book (Second ed.). Great Clarendon Street, Oxford, OX2 6DP, UK: Oxford University Press. ISBN   9780198351771.
4. Ramanathan, Anand; Robb, G. Brett; Chan, Siu-Hong (2016-09-19). "mRNA capping: biological functions and applications". Nucleic Acids Research. 44 (16): 7511–7526. doi: 10.1093/nar/gkw551 . ISSN   0305-1048. PMC   5027499 . PMID   27317694.
5. "Eukaryotic pre-mRNA processing". Khan Academy. Retrieved November 11, 2021.
6. Bienroth, S.; Keller, W.; Wahle, E. (February 1993). "Assembly of a processive messenger RNA polyadenylation complex". The EMBO Journal. 12 (2): 585–594. doi: 10.1002/j.1460-2075.1993.tb05690.x . PMC   413241 . PMID   8440247. S2CID   31439224.
7. Tian, Bin; Manley, James L. (January 2017). "Alternative polyadenylation of mRNA precursors". Nature Reviews Molecular Cell Biology. 18 (1): 18–30. doi:10.1038/nrm.2016.116. ISSN   1471-0072. PMC   5483950 . PMID   27677860.
8. Jo, Bong-Seok; Choi, Sun Shim (2015). "Introns: The Functional Benefits of Introns in Genomes". Genomics & Informatics. 13 (4): 112–8. doi:10.5808/GI.2015.13.4.112. PMC   4742320 . PMID   26865841.
9. Wilkinson, Max E.; Charenton, Clément; Nagai, Kiyoshi (2020-06-20). "RNA Splicing by the Spliceosome" . Annual Review of Biochemistry. 89 (1): 359–388. doi:10.1146/annurev-biochem-091719-064225. ISSN   0066-4154. PMID   31794245. S2CID   208626110.