U4 and neoplasm: This DU finger present in both USP4 and USP15 is responsible for the binding of squamous cell carcinoma antigen recognized by T-cells 3 (SART3), which is considered to be a U4/U6 small nuclear RNA recycling factor and also a tumor antigen usually recognized by the HLA-A24-restricted and tumor-specific cytotoxic T lymphocytes.