The proteins encoded by the human TPR-MET oncogene (p65tPr-mt) and the human MET protooncogene (p140O"') have been identified. The p65tPr-met and p44lt, as well as a truncated TPR-MET product expressed in Escherichia coli, p509et, are autophosphorylated in vitro on tyrosine residues. Using the immunocomplex kinase assay, p1404et activity was detected in various human tumor epithelial cell lines. In vivo, p65P'-pr-is phosphorylated on both serine and tyrosine residues, while pl4Ont is phosphorylated on serine and threonine. pl4et is labeled by cell-surface iodination procedures, suggesting that it is a receptor-like transmembrane proteintyrosine kinase.The MET oncogene was identified in a N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-treated human osteogenic sarcoma cell line, MNNG-HOS (1, 2), by using the murine NIH 3T3 cell transfection assay. We have shown that activation of the MET oncogene occurred via a chromosomal DNA rearrangement (3,4). This rearrangement created a hybrid TPR-MET gene with upstream sequences derived from a locus on chromosome 1 (designated TPR for translocated promoter region) fused to downstream sequences from the MET protooncogene locus located on chromosome 7, 7q21-31 (5). The MET protooncogene is predominantly expressed in human fibroblast and epithelial cell lines as a 9.0-kilobase (kb) RNA species, whereas the activated TPR-MET oncogene expresses a novel 5.0-kb TPR-MET hybrid RNA species (3). Nucleotide sequence analysis of the MET protooncogene cDNA revealed an open reading frame of 1408 amino acids with features characteristic of the growth factor receptor protein-tyrosine kinase family (6). The predicted primary structure contains a 926-amino acid external domain and a 435-amino acid cytoplasmic domain with homology to the protein-tyrosine kinase family of genes. We have used C-terminal anti-MET peptide antibodies to identify and characterize the TPR-MET oncogene and MET protooncogene protein products. Both p65tPr-met and p140met are protein-tyrosine kinases and undergo autophosphorylation in vitro. Expression of the MET Kinase Domain in Escherichia coli. The plasmid pBR5a, containing 2.1-kb TPR-MET human cDNA (6) was digested with HindIlI, and the resulting 1.6-kb cDNA fragment containing the MET kinase domain was inserted in frame at the unique HindIII site of pJLA16 (7) to generate plasmid pAMET-2. A 50-kDa protein (p5soe,) was expressed in bacterial cells containing pAMET-2 upon induction at 420C. The p5Oet was purified as described (7) and analyzed by NaDodSO4/polyacrylamide gel electrophoresis followed by staining with Coomassie blue or assayed in vitro for kinase activity. MATERIALS AND METHODSPreparation of MET-Specific Antisera. Three peptides corresponding to the predicted 8-, 16-, and 28-amino acids at the C terminus of the MET protein (5) were constructed by solid-phase Merrifield procedures (8) as described (9). Peptide coupled to keyhole limpet hemocyanin (9, 10) was mixed with Freund's complete adjuvant and administered subcutaneously into rabbits. Sera were...