EPH receptor A1 (EphA1), with 976-amino acid protein(about 107 kDa), belongs to the ephrin receptor subfamily of the protein-tyrosine kinase family. The Eph subfamily represents the largest group of receptor protein tyrosine kinases identified to date and their ligands, the ephrins,can be subdivided into two major subclasses, ephrin-A and ephrin-B. Interaction of Eph receptor tyrosine kinases with their membrane bound ephrin ligands initiates bidirectional signaling events that regulate cell migratory and adhesive behavior, particularly in the nervous system. They have been implicated in various developmental processes, including axonal guidance, angiogenesis, morphogenesis and carcinogenesis.