Contactin1 (CNTN1) is a member of the contactin subgroup within the immunoglobulin superfamily. It was originally designated contactin in human, F3 in rodents, and F11 in chicken. Other members of this family in human include Contactin2(TAG1), Contactin5 (NB2), and Contactin6 (NB3). Additional family members have been described in other species. CNTN1 shares less than 50% amino acid sequence identity with the other contactins. The human and rodent CNTN1 proteins share 96% sequence identity. The 998 amino acid mature protein contains 6 Iglike domains and 4 fibronectin type III like domains, and is attached to the membrane by a GPI anchor. CNTN1 is differentially expressed in numerous neuronal tissues and functions in nervous system development. It associates with two other cellsurface proteins believed to participate in signal transduction, receptor protein tyrosine phosphatase beta (RPTPβ) and Contactinassociated protein (Caspr). Reported ligands include NrCAM and the extracellular matrix glycoprotein, tenascin.