THE AXONAL RECOGNITION MOLECULE F11 IS A MULTIFUNCTIONAL PROTEIN - SPECIFIC DOMAINS MEDIATE INTERACTIONS WITH NG-CAM AND RESTRICTIN

F11 is a glycosyl phosphatidylinositol-anchored axonal surface glycopr otein belonging to a neural subgroup of the immunoglobulin superfamily . In this report, we demonstrate that the F11 protein displays three d istinguishable activities: binding to the cell recognition molecule Ng -CAM, interaction with the extracellular matrix glycoprotein restricti n (RN), and a neurite outgrowth-promoting activity. By analyzing delet ion mutants expressed in transfected COS cells, epitope mapping of mon oclonal antibodies, and neurite outgrowth assays, we reveal that these activities can be localized to distinct regions within the F11 protei n. The Ng-CAM-binding site resides in the first two immunoglobulin-lik e domains of F11, whereas the RN-binding site resides in the second or third domain. A neurite outgrowth-promoting activity of F11 character ized by in vitro culture of tectal cells is independent of F11-Ng-CAM and F11-RN binding.