Anti-U21.1 antibodies are used in antigen-specific immunodetection in biological samples. The target U21.1 is a known alias name of the protein heterogeneous nuclear ribonucleoprotein U, encoded by the HNRNPU gene in humans. This 825-amino acid residue protein is known to be involved in the cell cycle, among other biological processes. In terms of tissue expression, it is widely expressed across many tissue types. Other synonyms for U21.1 include DEE54, EIEE54, and GRIP120.