Polyadenylation

Definition

Polyadenylation is the process of adding a poly(A) tail, a stretch of adenine nucleotides, to the 3' end of a newly synthesized messenger RNA (mRNA) molecule. This modification plays a crucial role in mRNA stability, nuclear export, and translation efficiency, making it essential for proper gene expression and regulation in eukaryotic cells.

5 Must Know Facts For Your Next Test

1. Polyadenylation occurs co-transcriptionally, meaning it takes place while the mRNA is still being synthesized by RNA polymerase.
2. The length of the poly(A) tail can influence mRNA stability and translation; longer tails generally result in more stable mRNAs.
3. Polyadenylation is facilitated by specific sequences in the mRNA precursor, typically characterized by a polyadenylation signal followed by a cleavage site.
4. This process is crucial for preventing degradation of mRNA by exonucleases, which would otherwise target unprotected mRNAs.
5. Polyadenylation is a key step in the maturation of mRNA and is often coupled with other modifications such as capping and splicing.

Review Questions

• How does polyadenylation contribute to mRNA stability and translation efficiency?
  • Polyadenylation contributes to mRNA stability by adding a protective poly(A) tail to the 3' end of the mRNA molecule. This tail helps prevent degradation by exonucleases, which would otherwise degrade unprotected mRNAs. Additionally, a longer poly(A) tail enhances translation efficiency by facilitating the binding of ribosomes and other translation factors, thereby promoting protein synthesis.
• Discuss the significance of the polyadenylation signal and its role in the process of polyadenylation.
  • The polyadenylation signal is a specific nucleotide sequence found within the pre-mRNA that signals for the addition of the poly(A) tail. This signal typically consists of the sequence 'AAUAAA', which is recognized by proteins that bind to this region and mediate the cleavage of the RNA at a nearby site. Following cleavage, poly(A) polymerase adds adenine nucleotides to form the poly(A) tail, making this signal crucial for the proper processing of mRNA.
• Evaluate how defects in polyadenylation can lead to diseases and their implications for gene expression.
  • Defects in polyadenylation can result in unstable mRNAs or inefficient translation, leading to reduced protein levels or dysfunctional proteins. This can contribute to various diseases, including certain cancers and genetic disorders where altered gene expression plays a role. Understanding these defects can provide insights into therapeutic strategies aimed at correcting aberrant gene expression patterns or enhancing mRNA stability, thereby offering potential avenues for treatment.

Related terms

mRNA:

Messenger RNA (mRNA) is a type of RNA that conveys genetic information from DNA to the ribosome, where proteins are synthesized.

RNA polymerase: RNA polymerase is the enzyme responsible for synthesizing RNA from a DNA template during the process of transcription.

splicing: Splicing is the process by which introns are removed and exons are joined together in pre-mRNA to produce mature mRNA.