Department of Biological Chemistry, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan-
Abstract: In eukaryotes, shortening of the 3'-poly-A- tail is the rate-limiting step in the degradation of most mRNAs, and two major mRNA deadenylase complexes--Caf1-Ccr4 and Pan2-Pan3--play central roles in this process, referred to as deadenylation- However, the molecular mechanism triggering deadenylation remains elusive- Previously, we demonstrated that eukaryotic releasing factor eRF3 mediates deadenylation and decay of mRNA in a manner coupled to translation termination- Here, we report the mechanism of mRNA deadenylation- The eRF3-mediated deadenylation is catalyzed by both Caf1-Ccr4 and Pan2-Pan3- Interestingly, translation termination complexes eRF1-eRF3, Pan2-Pan3, and Caf1-Ccr4 competitively interact with polyadenylate-binding protein PABPC1- In each complex, eRF3, Pan3, and Tob, respectively, mediate PABPC1 binding, and a combination of a PAM2 motif and a PABC domain is commonly utilized for their contacts- A translation-dependent exchange of eRF1-eRF3 for the deadenylase occurs on PABPC1- Consequently, PABPC1 binding leads to the activation of Pan2-Pan3 and Caf1-Ccr4- From these results, we suggest a mechanism of mRNA deadenylation by Pan2-Pan3 and Caf1-Ccr4 in cooperation with eRF3 and PABPC1-