MOLECULAR-CLONING OF QUEK-1 AND QUEK-2, 2 QUAIL VASCULAR ENDOTHELIAL GROWTH-FACTOR (VEGF) RECEPTOR-LIKE MOLECULES

We have previously reported the cloning of two partial cDNAs correspon ding to two quail (Coturnix coturnix japonica) receptor tyrosine kinas es (RTKs), named Quek 1 and Quek 2, and their expression in endothelia l cells of the early avian embryo, We here report the cloning of the f ull-size cDNAs for both molecules. Sequence comparison shows that Quek 1 and 2 share an overall amino acid (aa) identity of 49%. They both c omprise seven extracellular immunoglobulin-like (Ig-like) domains, a s ingle transmembrane domain, and an intracellular kinase domain split i nto two by a 70 aa insertion. These structural characteristics are sha red by the members of the recently discovered VEGF receptor (VEGFR) fa mily. We have compared the sequences of Quek 1 and 2 to the other VEGF Rs. At the aa level, Quek 1 is most closely related to KDR/flk-1 (VEGF R 2) (aa identity of 69% and 71%, respectively). Quek 2 shows a simila r degree of aa identity to flt-4 (VEGFR 3). Quek 1 and 2 display a low er homology to flt-1 (VEGFR 1) (about 45% aa identity). These data sug gest that Quek 1 and 2 are the avian homologues of VEGFRs 2 and 3, res pectively.