Anti-nudix hydrolase 21 antibodies are used in the immunodetection of the protein encoded by the NUDT21 gene. In humans, the canonical protein has a reported length of 227 amino acid residues and a mass of 26.2 kDa. Its subcellular localization is in the nucleus and cytoplasm. It is reported to be expressed in the heart, brain, placenta, lung, liver, skeletal muscle, kidney and pancreas. A member of the Nudix hydrolase protein family, it is a known 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. Post-translational modifications have been described, including acetylation. Other names for this target antigen include CPSF5, cleavage and polyadenylation specificity factor subunit 5, CPSF 25 kDa subunit, and CFIM25.