Messenger RNA in Eukaryotes

Abstract

Posttranscriptional regulation of gene expression represents an important level at which eukaryotes can expand the coding capacity of their genomes. The concept that one gene makes one protein does not apply to higher eukaryotes. Thus, a eukaryotic cell can use alternative ribonucleic acid (RNA) splicing, alternative polyadenylation and RNA editing to produce hundreds or even several thousands of protein isoforms from a single gene.

Keywords: mRNA; splicing; polyadenylation; snRNP; hnRNP

Figure 1.

Coupling of RNA polymerase II transcription and RNA processing in higher eukaryotes. The C‐terminal domain (CTD) recruits RNA processing factors to the transcribing RNA polymerase. At the initiation phase of transcription the CTD binds factors required for capping of the nascent RNA chain. During the elongation phase the CTD binds and deposits RNA splicing factors along the transcript and factors required for cleavage and polyadenylation of the nascent transcript. Intron sequences are shown as wavy lines and protein‐coding exon sequences shown as boxes.

Figure 2.

The exon definition model. Exons in a pre‐mRNA are recognized as units by U2 snRNP (U2) binding to the 3′ splice site and U1 snRNP (U1) binding to the downstream 5′ splice site. Subsequently, adjacent exons are defined across the intron. In both recognition steps the conserved SR family of splicing factors function as bridging proteins.

Figure 3.

Pre‐mRNAs splicing is catalysed in large ribonucleoprotein complexes termed spliceosomes. The figure illustrates the sequential addition of U snRNPs into the spliceosome. In a first step U1 and U2 snRNPs, together with other non‐snRNP splicing factors, recognizes the exon–intron borders in the pre‐mRNA, thereby forming a pre‐spliceosome complex. The mature spliceosome is formed after addition of the triple U4/U6/U5 snRNP. Boxes represent exons and the intron is shown as a thin line.

Figure 4.

Different alternative splicing pathways. Illustrated are the different ways pre‐mRNAs can be alternatively spliced: (a) by combining alternative 5′ splice sites with a common 3′ splice site, (b) by combining alternative 3′ splice sites with a common 5′ splice site, (c) exon inclusion or skipping, (d) usage of mutually exclusive splice sites. Exon sequences are shown as large boxes and intron sequences as wavy lines.

Figure 5.

mRNP assembly and nucleocytoplasmic transport. The figure illustrates how pre‐mRNAs and mRNAs in eukaryotes immediately become associated with proteins upon transcription, forming mRNP, which is then partly dissociated upon transport through the nuclear pore into the cytoplasm.

Figure 6.

The relationship between viral and cellular mRNA export. Panel a illustrates how normal cellular mRNAs use the general nuclear export receptor TAP to connect to the nuclear pore complex. The figure also illustrates how (b) HSV‐1, (c) Mason‐Pfizer monkey virus and (d) HIV highjack the cellular mRNA and U‐snRNA export machineries to stimulate virus‐specific mRNA export.

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Further Reading

Black DL (2003) Mechanisms of alternative pre‐messenger RNA splicing. Annual Review of Biochemistry 72: 291–336.

Chang Y‐F, Imam JS and Wilkinson MF (2007) The nonsense‐mediated decay RNA surveillance pathway. Annual Review of Biochemistry 76: 15.1–15.24.

Dreyfuss G, Kim VN and Kataoka N (2002) Messenger‐RNA‐binding proteins and the messages they carry. Nature Reviews Molecular Cell Biology 3: 195–205.

Huang Y and Steitz JA (2005) Surprises along a messenger's journey. Molecular Cell 17: 613–615.

Maniatis T and Reed R (2002) An extensive network of coupling among gene expression machines. Nature 416: 499–506.

Nishikura K (2006) Editor meets silencer: crosstalk between RNA editing and RNA interference. Nature Reviews Molecular Cell Biology 7: 919–931.

Petersen‐Mahrt S (2005) DNA deamination in immunity. Immunology Review 203: 80–97.

Proudfoot N (2004) New perspectives on connecting messenger RNA 3′ end formation to transcription. Current Opinion in Cell Biology 16: 272–278.

Sandri‐Goldin RM (2004) Viral regulation of mRNA export. Journal of Virology 78: 4389–4396.

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How to Cite close
Akusjärvi, Göran, Kreivi, Jan‐Peter, and Petersen‐Mahrt, Svend(Dec 2007) Messenger RNA in Eukaryotes. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000875.pub2]