Characterization of the human full-length PTK7 cDNA encoding a receptor protein tyrosine kinase-like molecule closely related to chick KLG.

A 220-bp fragment of PTK7 cDNA was previously cloned from normal human melanocyte RNAs by means of the reverse transcription-polymerase chain reaction [Lee, S.-T., Strunk, K.M., and Spritz, R.A. (1993) Oncogene 8, 3403-3410]. We now report the cloning of the human full-length PTK7 cDNA and its characterization. The 1,070 amino acid PTK7 polypeptide deduced from the cDNA sequence constitutes receptor protein tyrosine kinase (RPTK), but has several unusual residues in some of the highly conserved tyrosine kinase motifs. PTK7 mRNA was expressed at the highest level in a human erythroleukemia cell line among tested samples, and at relatively high levels in liver, lung, pancreas, kidney, placenta, and melanocytes. Human PTK7 is 72% identical to chick KLG, suggesting that PTK7 is homologous or possibly orthologous to chick KLG, and that these represent a new subfamily of RPTKs.