1. Integration of transfected LTR sequences into the c-raf proto-oncogene: activation by promoter insertion.
- Author
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Mölders H, Defesche J, Müller D, Bonner TI, Rapp UR, and Müller R
- Subjects
- Animals, Base Sequence, Cells, Cultured, Cloning, Molecular, DNA, Viral genetics, Gene Amplification, Gene Expression Regulation, Genetic Linkage, Mice, Promoter Regions, Genetic, Repetitive Sequences, Nucleic Acid, Transcription, Genetic, Cell Transformation, Neoplastic, Moloney murine leukemia virus genetics, Oncogenes
- Abstract
A malignant cell line (clone S1) isolated after co-transfection of normal NIH3T3 DNA and Moloney leukemia virus long terminal repeat (Mo-LTR) sequences has previously been described to contain an activated c-raf oncogene. Here, we report the isolation by molecular cloning and the structural analysis of the LTR-activated c-raf gene. As shown by Southern blot and nucleotide sequence analyses, the transfected Mo-LTR sequences integrated into the 5th intron of the endogenous c-raf proto-oncogene. This intragenic LTR insertion led to the expression of high levels of LTR-U5-c-raf hybrid transcripts indicating an initiation of transcription from the Mo-LTR promoter. Transcriptional activation of c-raf is accompanied by the synthesis of large amounts of cytoplasmic c-raf protein. Immunoblot analysis suggests that the proteins encoded by the LTR-activated c-raf gene are truncated compared with the normal c-raf gene product(s). Our results indicate a promoter insertion mechanism of c-raf activation.
- Published
- 1985
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