FIGURE 4.

Stabilization of polyadenylated mRNAs. During their lifetime, the mRNA poly(A) tails become gradually shortened through CCR4‐NOT‐mediated deadenylation (center) that later leads to complete mRNA degradation from both ends (not shown). TENT4A/B enhances the stability of mRNAs by the mixed A/G tailing of their poly(A) tails (on the left). The guanosine residues in the terminal positions of poly(A) tails protect mRNA from deadenylation by CCR4‐NOT because CCR4‐NOT is unable to efficiently remove the guanidine residue. Proteins from the TENT5 family elongate mRNA poly(A) tails in the cytoplasm, ultimately extending the mRNA lifespan and enhancing its expression (on the right). Remaining unknown are the ways in which TENT4 and TENT5 ncPAPs recognize their target RNA and whether other protein cofactors facilitate their function