Which enzyme is responsible for shortening the poly-A tail in the mRNA degradation process?

The enzyme responsible for shortening the poly-A tail during the mRNA degradation process is deadenylase. This enzyme specifically targets the poly-A tail, which is a stretch of adenine nucleotides added to the 3' end of eukaryotic mRNA molecules. The deadenylase gradually removes these adenine residues, leading to a decrease in the stability of the mRNA. As the poly-A tail shortens, it becomes more susceptible to further degradation and ultimately facilitates the mRNA's decapping and subsequent dismantling by exonucleases.

The other options do not serve this specific function in the mRNA degradation pathway. Proteases are primarily involved in degrading proteins rather than RNA. The decapping enzyme removes the cap structure at the 5' end of the mRNA, which is a different step in the degradation process following the shortening of the poly-A tail. Adenylase, on the other hand, is typically not associated with the degradation process but rather with adding adenine residues in RNA synthesis contexts. This understanding of the roles of these enzymes is critical for grasping the intricacies of gene expression regulation and mRNA turnover.