Anti-Sr protein antibodies enable researchers to detect and measure the Sr protein antigen in biological samples. This target is a reported synonym of the RNPS1 gene, which encodes RNA binding protein with serine rich domain 1. This protein is known to function in RNA splicing and the regulation of apoptosis, among other biological roles. The human version of Sr protein has a canonical amino acid length of 305 residues and a protein mass of 34.2 kilodaltons, although 3 isoforms have been identified. It is reported to be localized in the nucleus and cytoplasm of cells and notably expressed in the hippocampus, duodenum, cerebral cortex, cerebellum, and caudate. Other names for this target antigen include E5.1, RNA binding protein with serine-rich domain, and RNA-binding protein S1, serine-rich domain.