Polyadenylation

Polyadenylation is a process in molecular biology that involves the addition of a poly(A) tail to a messenger RNA (mRNA) molecule. This process is crucial for the stability, export, and translation of mRNA.

Process

Polyadenylation occurs in the nucleus after the transcription process. The newly synthesized mRNA, known as pre-mRNA, undergoes several modifications, including 5' capping, splicing, and polyadenylation.

The polyadenylation process begins with the cleavage of the pre-mRNA molecule at the polyadenylation site, which is usually a sequence of adenine and uracil bases. This cleavage is facilitated by a complex of proteins known as the cleavage and polyadenylation specificity factor (CPSF) and the cleavage stimulation factor (CstF).

Following cleavage, an enzyme called poly(A) polymerase adds a series of adenine bases to the 3' end of the mRNA. This poly(A) tail can be up to 250 bases long in eukaryotes and serves several functions, including protection of the mRNA molecule from degradation, facilitation of its export from the nucleus, and promotion of its translation into protein.

Role in Gene Expression

Polyadenylation plays a crucial role in gene expression. The length of the poly(A) tail can influence the stability and translation efficiency of the mRNA. Shortening of the poly(A) tail, a process known as deadenylation, can lead to the degradation of the mRNA and thus termination of its translation into protein.

In addition, polyadenylation can also influence the choice of alternative polyadenylation sites, which can result in the production of different protein isoforms from the same gene. This adds another layer of complexity to the regulation of gene expression.

See Also

• RNA splicing
• Transcription (biology)
• Translation (biology)

References

• Polyadenylation
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  Structure of mRNA
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  Chemical structure of adenine in RNA
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  Diagram of alternative polyadenylation
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  Bacterial PNPase and polyadenylation process