RSE, A NOVEL RECEPTOR-TYPE TYROSINE KINASE WITH HOMOLOGY TO AXL UFO, IS EXPRESSED AT HIGH-LEVELS IN THE BRAIN/

We have isolated cDNA clones that encode the human and murine forms of a novel receptor-type tyrosine kinase termed Rse. Sequence analysis i ndicates that human Rse contains 890 amino acids, with an extracellula r region composed of two immunoglobulin-like domains followed by two f ibronectin type III domains. Murine Rse contains 880 amino acids and s hares 90% amino acid identity with its human counterpart. Rse is struc turally similar to the receptor-type tyrosine kinase Axl/Ufo, and the two proteins have 35 and 63% sequence identity in their extracellular and intracellular domains, respectively. To study the synthesis and ac tivation of this putative receptor-type tyrosine kinase, we constructe d a version of Rse (termed gD-Rse, where go represents glycoprotein D) that contains an NH2-terminal epitope tag NM3T3 cells were engineered to express gD-Rse, which could be detected at the cell surface by flu orescence-activated cell sorting. Moreover, gD-Rse was rapidly phospho rylated on tyrosine residues upon incubation of the cells with an anti body directed against the epitope tag, suggesting that rse encodes an active tyrosine kinase. in the human tissues we examined, the highest level of expression of rse mRNA was observed in the brain; rse mRNA wa s also detected in the premegakaryocytopoietic cell lines CMK11-5 and Dami. The gene for rse was localized to human chromsome 15.