Catalytic subunit of the poly(A)-nuclease (PAN) deadenylation complex, one of two cytoplasmic mRNA deadenylases involved in mRNA turnover. PAN specifically shortens poly(A) tails of RNA and the activity is stimulated by poly(A)-binding protein pab1. PAN deadenylation is followed by rapid degradation of the shortened mRNA tails by the CCR4-NOT complex. Deadenylated mRNAs are then degraded by two alternative mechanisms, namely exosome-mediated 3'-5' exonucleolytic degradation, or deadenlyation-dependent mRNA decaping and subsequent 5'-3' exonucleolytic degradation by xrn1. May also be involved in post-transcriptional maturation of mRNA poly(A) tails. Exonucleolytic cleavage of poly(A) to 5'-AMP. Binds 2 metal cations per subunit in the catalytic exonuclease domain. Positively regulated by the regulatory subunit ppk26/pan3. Forms a heterotrimer with an asymmetric homodimer of the regulatory subunit ppk26/pan3 to form the poly(A)-nuclease (PAN) deadenylation complex. Contains a pseudo-UCH domain. This ubiquitin C-terminal hydrolase (UCH)-like or ubiquitin specific protease (USP)-like domain is predicted to be catalytically inactive because it lacks the active site catalytic triad characteristic of thiol proteases, with residues at the equivalent structural positions that are incompatible with catalysis, and it cannot bind ubiquitin. It functions as a structural scaffold for intra- and intermolecular interactions in the complex. The linker, or PAN3 interaction domain (PID), between the WD40 repeats and the pseudo-UCH domain mediates interaction with ppk26/pan3. Belongs to the peptidase C19 family. PAN2 subfamily.