Ephrin A4 is also known as LERK4 or ELF4. Ephrin A4 binds EphA2, EphA3, EphA4, EphA5, EphA6, EphA7, and EphB1. To date, at least 14 members of the Eph receptor family and a family of 8 ligands have been identified. Ligands of Eph family receptors are structurally related membrane bound proteins that can be subdivided into two major subclasses: ephrin A and ephrin B. Ligands in the ephrin A subclass, including the prototype family member ephrin A1 (B61), are membrane associated through glycosylphosphatidyl inositollinkages; whereas ephrin B subclass consists of ligands with transmembrane domains. The general role of the Eph family is in mediating repulsive cell to cell interaction, as suggested by studies of axonal guidance and neural crest cell migration.