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.