Component of the cleavage factor Im (CFIm) complex that functions as an activator of the pre-mRNA 3'-end cleavage and polyadenylation processing required for the maturation of pre-mRNA into functional mRNAs (PubMed:9659921, PubMed:8626397, PubMed:14690600, PubMed:15937220, PubMed:17024186, PubMed:17098938, PubMed:29276085). CFIm contributes to the recruitment of multiprotein complexes on specific sequences on the pre-mRNA 3'-end, so called cleavage and polyadenylation signals (pA signals) (PubMed:9659921, PubMed:8626397, PubMed:14690600, PubMed:17024186). Most pre-mRNAs contain multiple pA signals, resulting in alternative cleavage and polyadenylation (APA) producing mRNAs with variable 3'-end formation (PubMed:17098938, PubMed:23187700, PubMed:29276085). The CFIm complex acts as a key regulator of cleavage and polyadenylation site choice during APA through its binding to 5'-UGUA-3' elements localized in the 3'-untranslated region (UTR) for a huge number of pre-mRNAs (PubMed:17098938, PubMed:20695905, PubMed:29276085). NUDT21/CPSF5 activates indirectly the mRNA 3'-processing machinery by recruiting CPSF6 and/or CPSF7 (PubMed:29276085). Binds to 5'-UGUA-3' elements localized upstream of pA signals that act as enhancers of pre-mRNA 3'-end processing (PubMed:8626397, PubMed:14690600, PubMed:15169763, PubMed:17024186, PubMed:22813749, PubMed:20479262). The homodimer mediates simultaneous sequence-specific recognition of two 5'-UGUA-3' elements within the pre-mRNA (PubMed:20479262, PubMed:21295486). Plays a role in somatic cell fate transitions and pluripotency by regulating widespread changes in gene expression through an APA-dependent function (By similarity). Binds to chromatin (By similarity). Binds to, but does not hydrolyze mono- and di-adenosine nucleotides (PubMed:18445629). Homodimer (via N- and C-terminus); binds RNA as homodimer (PubMed:20695905, PubMed:18445629, PubMed:20479262). Component of the cleavage factor Im (CFIm) complex which is a heterotetramer composed of two subunits of NUDT21/CPSF5 and two subunits of CPSF6 or CPSF7 or a heterodimer of CPSF6 and CPSF7 (PubMed:9659921, PubMed:8626397, PubMed:14561889, PubMed:20695905, PubMed:23187700, PubMed:21295486). The cleavage factor Im (CFIm) complex associates with the CPSF and CSTF complexes to promote the assembly of the core mRNA 3'-processing machinery (PubMed:29276085). Interacts with CPSF6 (via the RRM domain); this interaction is direct and enhances binding to RNA (PubMed:14561889, PubMed:15169763, PubMed:17172643, PubMed:19864460, PubMed:29276085). Interacts with CPSF7 (PubMed:29276085, Ref.30). Interacts with FIP1L1; this interaction occurs in a RNA sequence-specific manner (PubMed:15937220). Interacts with PABPN1 (PubMed:15169763). Interacts (via N-terminus) with PAPOLA (via C-terminus); this interaction is direct and diminished by acetylation (PubMed:15169763, PubMed:17172643). Interacts with SNRNP70 (PubMed:14561889). Interacts with VIRMA (PubMed:29507755). Shuttles between the nucleus and the cytoplasm in a transcription- and XPO1/CRM1-independent manner, most probably in complex with the cleavage factor Im complex (CFIm) (PubMed:19864460). In punctate subnuclear structures localized adjacent to nuclear speckles, called paraspeckles (PubMed:15169763). Expressed in the heart, brain, placenta, lung, liver, skeletal muscle, kidney and pancreas. Acetylated mainly by p300/CBP, recruited to the complex by CPSF6. Acetylation decreases interaction with PAPAO. Deacetylated by the class I/II HDACs, HDAC1, HDAC3 and HDAC10, and by the class III HDACs, SIRT1 AND SIRT2. Belongs to the Nudix hydrolase family. CPSF5 subfamily. Lacks the conserved metal-binding residues in the NUDIX motif and does not have hydrolase activity.