Anti-Ki-1/57 antibodies enable researchers to detect and measure the Ki-1/57 antigen in biological samples. This target is a reported synonym of the HABP4 gene, which encodes hyaluronan binding protein 4. This protein is known to function in mRNA processing and RNA splicing, among other biological roles. The human version of Ki-1/57 has a canonical amino acid length of 413 residues and a protein mass of 45.8 kilodaltons, although 2 isoforms have been identified. It is reported to be localized in the nucleus and cytoplasm of cells and notably expressed in many tissues, such as the cerebral cortex and placenta.