Shortening and removal of the 3' poly(A) tail of mature mRNA by poly(A)-specific 
3' exonucleases (deadenylases) is the initial and often rate-limiting step in 
mRNA degradation. The majority of cytoplasmic deadenylase activity is associated 
with the Ccr4-Not and Pan2-Pan3 complexes. Two distinct catalytic subunits, 
Caf1/Pop2 and Ccr4, are associated with the Ccr4-Not complex, whereas the Pan2 
enzymatic subunit forms a stable complex with Pan3. In this review, we discuss 
the composition and activity of these two deadenylases. In addition, we comment 
on generic and specific mechanisms of recruitment of Ccr4-Not and Pan2-Pan3 to 
mRNAs. Finally, we discuss specialised and redundant functions of the 
deadenylases and review the importance of Ccr4-Not subunits in the regulation of 
physiological processes. This article is part of a Special Issue entitled: RNA 
Decay mechanisms.