mRNA poly(A) tails affect translation, mRNA export and mRNA stability, with 
translation initiation involving a direct interaction between eIF4G and the 
poly(A)-binding protein Pab1. The latter factor contains four RNA recognition 
motifs followed by a C-terminal region composed of a linker and a PABC domain. 
We show here that yeast mutants lacking the C-terminal domains of Pab1 display 
specific synthetic interactions with mutants in the 5'-3' mRNA decay pathway. 
Moreover, these mutations impair mRNA decay in vivo without significantly 
affecting mRNA export or translation. Inhibition of mRNA decay occurs through 
slowed deadenylation. In vitro analyses demonstrate that removal of the Pab1 
linker domain directly interferes with the ability of the Pop2-Ccr4 complex to 
deadenylate the Pab1-bound poly(A). Binding assays demonstrate that this results 
from a modulation of poly(A) packaging by the Pab1 linker region. Overall, our 
results demonstrate a direct involvement of Pab1 in mRNA decay and reveal the 
modular nature of this factor, with different domains affecting various cellular 
processes. These data suggest new models involving the modulation of poly(A) 
packaging by Pab1 to control mRNA decay.