Figure 4

Roles of PABP in mRNA translation and stability. This model depicts different stages of a cytoplasmic mRNA 'life cycle', in which distinct roles can be ascribed to PABP. (a) Association of PABP with the mRNA poly(A) tail. (b) Interaction of PABP with elongation initiation factor eIF4G to promote formation of the 'closed loop', thus (c) initiating translation and antagonizing decapping. (d) Interaction of PABP with the termination factor eRF3 and recycling of the ribosome from the 5' to the 3' end of the same mRNA. (e) Poly(A) shortening by the Ccr4p-Pop2p-Notp deadenylase complex. (f) Loss of the poly(A) tail and PABP, facilitating (g) dissociation of the proteins of the mRNP, binding of the Lsm1-7p-Pat1p complex, and decapping by the decapping proteins Dcp1p and Dcp2p, and subsequent (h) 5'-to-3' degradation of the mRNA by the exonuclease Xrn1p or (i) 3'-to-5' degradation by the exosome.