MOLECULAR-CLONING OF 2 NOVEL TRANSMEMBRANE LIGANDS FOR EPH-RELATED KINASES (LERKS) THAT ARE RELATED TO LERK-2

A search of the nucleic acid database of expressed sequence rags (ESTs ) revealed several partial cDNA sequences that could encode proteins h omologous to the ligands for Eph-related kinases (LERKs). Oligonucleot ides designed from the ESTs were used to probe a human brain cDNA libr ary and obtain overlapping clones that encoded two different novel LER KS (NLERK-1 and NLERK-2). NLERK-1 and NLERK-2 are most closely related to human LERK-2/Elk-ligand and they form a subclass of LERKs that con tain a transmembrane domain and a conserved cytoplasmic domain. Full-l ength NLERK-1 was expressed as a glycosylated membrane protein in COS cells and was not secreted into the medium. Full-length NLERK-2 was si milarly expressed in COS cells but both membrane-bound and a truncated , proteolytically- released form were detected. Engineered forms of bo th NLERK-1 and NLERK-2 lacking transmembrane and cytoplasmic domains w ere also expressed in COS cells and each was detected in the extracell ular medium.