Question

Explain why decapping and deadenylation are common mechanisms involved in RNA decay.

Short answer

Answer: Decapping and deadenylation are two mechanisms that facilitate the degradation of messenger RNA (mRNA) molecules in cells. Decapping is a process in which the 5' cap structure of an mRNA molecule is removed, exposing the mRNA to exonucleases for degradation. Deadenylation is the process of removing the poly(A) tail from the 3' end of an mRNA molecule, weakening its protection and making it more susceptible to degradation. These processes cooperate to ensure efficient mRNA degradation, contributing to cellular homeostasis and the regulation of gene expression.

Step-by-step solution

Introduction

In eukaryotic cells, messenger RNA (mRNA) plays a crucial role in conveying genetic information from the DNA in the nucleus to the ribosomes in the cytoplasm for protein synthesis. However, mRNA molecules are not meant to last indefinitely – they are eventually degraded to maintain cellular homeostasis and regulate gene expression. Two common mechanisms involved in mRNA decay are decapping and deadenylation.

Decapping

Decapping is a process in which the 5' cap structure of an mRNA molecule is removed. The 5' cap is a modified guanine nucleotide that protects the mRNA from degradation by exonucleases and promotes mRNA stability. By removing the 5' cap, decapping exposes the mRNA to exonucleases, which rapidly degrade the mRNA molecule from the 5' end. Thus, decapping acts as a "trigger" for mRNA degradation by exposing the vulnerable ends of the mRNA molecule to cellular exonucleases.

Deadenylation

Deadenylation is the process of removing the poly(A) tail from the 3' end of an mRNA molecule. The poly(A) tail is a long stretch of adenine nucleotides added to the 3' end of an mRNA molecule, playing a key role in protecting the mRNA from degradation by exonucleases and promoting mRNA stability. Deadenylation shortens the poly(A) tail, weakening the protection it provides and making the mRNA more susceptible to degradation by 3' to 5' exonucleases. Furthermore, deadenylation decreases the mRNA's affinity for poly(A) binding proteins (PABPs), which can also destabilize the mRNA transcript.

Mutual Cooperation Between Decapping and Deadenylation

Decapping and deadenylation often occur together in mRNA decay pathways, as they both facilitate mRNA degradation by targeting the protective features of the mRNA molecule. Deadenylation typically occurs before decapping, as it weakens the mRNA's structure, making it more susceptible to decapping and degradation. Thus, decapping and deadenylation cooperate to ensure efficient mRNA degradation and to maintain proper gene expression levels within the cell.

Conclusion

In conclusion, decapping and deadenylation are common mechanisms involved in RNA decay because they target the protective features of mRNA molecules, facilitating their degradation. By working together, these processes ensure efficient mRNA degradation, contributing to cellular homeostasis and the regulation of gene expression.