The protein encoded by this gene is a member of the immunoglobulin superfamily. The protein contains two immunoglobulin domains and thirteen fibronectin type III domains. Fibronectin type III domains are present in both extracellular and intracellular proteins and tandem repeats are known to contain binding sites for DNA, heparin and the cell surface. This protein, and a homologous mouse sequence, are very similar to the Drosophila sidekick gene product but the specific function of this superfamily member is not yet known. Evidence for alternative splicing at this gene locus has been observed but the full-length nature of additional variants has not yet been determined.
Nagase T, Kikuno R, Ishikawa K, et al. (2000). "Prediction of the coding sequences of unidentified human genes. XVII. The complete sequences of 100 new cDNA clones from brain which code for large proteins in vitro". DNA Res. 7 (2): 143–50. doi:10.1093/dnares/7.2.143. PMID10819331.
Nguyen DN, Liu Y, Litsky ML, Reinke R (1997). "The sidekick gene, a member of the immunoglobulin superfamily, is required for pattern formation in the Drosophila eye". Development. 124 (17): 3303–12. PMID9310325.