Precursor mRNA

Pre-mRNA is the first form of RNA created through transcription in protein synthesis. The pre-mRNA lacks structures that the messenger RNA (mRNA) requires. First all introns have to be removed from the transcribed RNA through a process known as splicing. Before the RNA is ready for export, a Poly(A)tail is added to the 3’ end of the RNA and a 5’ cap is added to the 5’ end.

See main article Primary transcript for more details

Precursor mRNA (pre-mRNA) is an immature single strand of messenger ribonucleic acid (mRNA). Pre-mRNA is synthesized from a DNA template in the cell nucleus by transcription. Pre-mRNA comprises the bulk of heterogeneous nuclear RNA (hnRNA). The term hnRNA is often used as a synonym for pre-mRNA, although, in the strict sense, hnRNA may include nuclear RNA transcripts that do not end up as cytoplasmic mRNA.

Once pre-mRNA has been completely processed, it is termed "mature messenger RNA", or simply "messenger RNA".

Processing

Eukaryotic pre-mRNA exists only briefly before it is fully processed into mRNA. Pre-mRNAs are build from 5'UTRs (directly upstream from the initiation codon), different number of exons and introns and 3'UTRs which immediately follows the translation termination codon. Exons are segments that are retained in the final mRNA, whereas introns are removed in a process called splicing, which is performed by the spliceosome (except for self-splicing introns).

Additional processing steps attach modifications to the 5' and 3' ends of Eukaryotic pre-mRNA. These include a 5' cap of 7-methylguanosine and a poly-A tail. In addition, eukaryotic pre-mRNAs have their introns spliced out by spliceosomes made up of small nuclear ribonucleoproteins.^[1]^[2]

When a pre-mRNA strand has been properly processed to an mRNA sequence, it is exported out of the nucleus and eventually translated into a protein – a process accomplished in conjunction with ribosomes.

References

↑ Weaver, Robert F. (2005). Molecular Biology, p.432-448. McGraw-Hill, New York, NY. ISBN 0-07-284611-9.
↑ Wahl, M. C.; Will, C. L.; Lührmann, R. (2009). "The Spliceosome: Design Principles of a Dynamic RNP Machine". Cell. 136 (4): 701–718. doi:10.1016/j.cell.2009.02.009. PMID 19239890.

External links

Scienceden.com RNA Article

Post-transcriptional modification

Nuclear

Precursor mRNA
5′ cap formation
Polyadenylation
- CPSF
- CstF
- PAP
- PAB2
- CFI
- CFII
Poly(A)-binding protein
RNA editing
Polyuridylation

RNA splicing

Intron / Exon snRNP Spliceosome minor U1 Alternative splicing

pre-mRNA factors	PLRG1 PRPF3 PRPF4 PRPF4B PRPF6 PRPF8 PRPF18 PRPF19 PRPF31 PRPF38A PRPF38B PRPF39 PRPF40A PRPF40B

Cytosolic

5′ cap methylation
mRNA decapping
- DCP1A
- DCP1B
- DCP2
- DCPS
- EDC3
- EDC4

Types of nucleic acids

Constituents

Ribonucleic acids
(coding, non-coding)

Translational	Messenger precursor, heterogenous nuclear Transfer Ribosomal Transfer-messenger

Regulatory	Interferential Micro Small interfering Piwi-interacting Antisense Processual Small nuclear Small nucleolar Small Cajal Body RNAs Y RNA Enhancer RNAs

Others	Guide Ribozyme Small hairpin Small temporal Trans-acting small interfering Subgenomic messenger

Deoxyribonucleic acids

Analogues

Cloning vectors

Phagemid
Plasmid
Lambda phage
Cosmid
Fosmid
Artificial chromosomes
- P1-derived
- Bacterial
- Yeast
- Human

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