Identification of receptor tyrosine kinases in the embryonic chicken lens

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Abstract
Protein phosphorylation plays a critical role in the control of growth and regulation of many eukaryotic cells. Members of the protein tyrosine kinase (PTK) family of peptides function as growth factor receptors and oncoproteins. A common feature of members of the PTK family is a highly conserved intracellular catalytic domain. We analyzed the chicken lens epithelium, which responds to several known growth factors, for the presence of receptor PTK's. Using reverse transcription polymerase chain reaction (rtPCR) and degenerate primers made to conserved regions within kinase domains, we amplified RNA from embryonic day 6 (E6) lens epithelium and sequenced 135 cDNA clones. Sixteen distinct kinase sequences were obtained. Eight of these sequences represented kinase domains of known mammalian growth factor receptors, and six represented intercellular kinases. Two sequences appeared to code for new kinases. The amino acid identity of the chicken homologs ranged from 80-100% when compared to their mammalian counterparts.