CHARACTERIZATION OF THE SEK-1 RECEPTOR TYROSINE KINASE

We present an initial characterisation of the mouse Sek-1 protein, a m ember of the Eph subfamily of putative receptor tyrosine kinases, whic h has been proposed to play a role in the segmentation of both the hin dbrain and the mesoderm, Antibodies raised against the protein have be en used to confirm the early embryonic expression pattern previously e stablished by mRNA in situ hybridisation. These antibodies, together w ith the expression of the Sek-1 gene in a baculovirus system, were ins trumental in demonstrating that the protein carries a tyrosine kinase activity and that it is presented at the cell surface with its N-termi nal (putative ligand-binding) domain outside of the cell, Therefore, a s expected from its amino acid sequence, Sek-1 conforms to the general model of receptor-type tyrosine kinases.