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 mRNA molecule. This modification plays a crucial role in stabilizing mRNA, facilitating its export from the nucleus to the cytoplasm, and enhancing its translation into proteins. By modifying RNA molecules in this way, cells regulate gene expression and ensure that only fully processed transcripts are translated into functional proteins.

5 Must Know Facts For Your Next Test

1. Polyadenylation typically occurs during the transcription process when RNA polymerase II synthesizes pre-mRNA.
2. The length of the poly(A) tail can vary among different mRNAs, influencing their stability and translational efficiency.
3. Specific enzymes, such as poly(A) polymerase, are responsible for adding the poly(A) tail to the mRNA.
4. Polyadenylation signals within the mRNA sequence guide the addition of the poly(A) tail, which usually follows a consensus sequence known as the polyadenylation signal.
5. Defects in polyadenylation can lead to various diseases, including certain types of cancer and genetic disorders due to improper gene expression regulation.

Review Questions

• How does polyadenylation affect the stability and translation of mRNA?
  • Polyadenylation enhances the stability of mRNA by adding a poly(A) tail, which protects the mRNA from degradation by exonucleases. A longer poly(A) tail generally leads to increased stability and improved translation efficiency since it helps recruit ribosomes for protein synthesis. This means that mRNAs with well-formed poly(A) tails are more likely to be translated into functional proteins compared to those without or with shorter tails.
• Discuss the mechanisms involved in the process of polyadenylation and how they influence RNA processing.
  • The process of polyadenylation involves several key steps, including recognition of the polyadenylation signal within pre-mRNA, recruitment of specific factors such as cleavage and polyadenylation specificity factor (CPSF), and the action of poly(A) polymerase to add adenine nucleotides. This intricate mechanism ensures that only properly processed mRNAs receive a poly(A) tail, which is vital for their stability and subsequent translation. Moreover, polyadenylation also interacts with other RNA processing events, such as splicing, indicating that multiple modifications work together to produce functional mRNA.
• Evaluate the implications of altered polyadenylation patterns in human diseases, providing examples.
  • Altered patterns of polyadenylation can have significant implications in human diseases by affecting gene expression regulation. For instance, certain cancers have been linked to abnormal polyadenylation events leading to unstable mRNAs that promote oncogene expression or hinder tumor suppressor gene function. Additionally, genetic disorders like spinal muscular atrophy have been associated with defective polyadenylation processes that disrupt normal RNA processing. These examples highlight how critical proper polyadenylation is for maintaining cellular homeostasis and how its disruption can contribute to disease development.

Related terms

mRNA:

Messenger RNA (mRNA) is a type of RNA that carries genetic information from DNA to the ribosome, where it serves as a template for protein synthesis.

RNA splicing: RNA splicing is the process of removing introns and joining exons in a pre-mRNA transcript to produce a mature mRNA molecule ready for translation.

5' cap:

The 5' cap is a modified guanine nucleotide added to the 5' end of an mRNA molecule that protects it from degradation and assists in ribosome binding during translation.