Has 3'-5' poly(A) exoribonuclease activity for synthetic poly(A) RNA substrate. Catalytic component of the CCR4-NOT complex which is one of the major cellular mRNA deadenylases and is linked to various cellular processes including bulk mRNA degradation, miRNA-mediated repression, translational repression during translational initiation and general transcription regulation. During miRNA-mediated repression the complex seems also to act as translational repressor during translational initiation. Additional complex functions may be a consequence of its influence on mRNA expression (By similarity). Exonucleolytic cleavage of poly(A) to 5'-AMP. Binds 2 divalent metal cations per subunit with RNAase activity being higher in presence of Mn(2+) than of Mg(2+) or Co(2+). Component of the CCR4-NOT complex. Belongs to the CAF1 family.