NUDT21, also known as CPSF5 or CFIm25, is a member of the Nudix hydrolase family of pyrophosphatases. This protein localizes to the paraspeckles and forms a heterodimer with CPSF6 or CPSF7 to comprise the CFIm (mammalian cleavage factor I) complex. NUDT21 is the smaller subunit of the complex and is present in all heterodimer combinations. NUDT21 plays an important role in pre-mRNA 3' cleavage and polyadenylation processing.