ret transforming gene encodes a fusion protein homologous to tyrosine kinases.

The ret transforming gene was activated by recombination between two unlinked segments of human DNA, most likely during transfection of NIH 3T3 cells. To further define this transforming gene, we isolated and sequenced ret cDNA clones. The nucleotide sequence indicates that the active ret transforming gene encodes a fusion protein with a carboxy-terminal domain which is 40 to 50% homologous to members of the tyrosine kinase gene family. This tyrosine kinase domain is preceded by a hydrophobic sequence characteristic of a transmembrane domain. Transcription of the ret tyrosine kinase sequence was detected in the SK-N-SH neuroblastoma, HL-60 promyelocytic leukemia, and THP-1 monocytic leukemia cell lines, but not in 25 other human tumor cell lines surveyed. The ret tyrosine kinase may thus represent a cell surface receptor which is expressed in a restricted range of human cells.