Identification by a random linker insertion method of a region which suppresses the transforming activity of the raf oncogene.

Activation mechanism of raf oncogene was studied by applying in vitro mutagenesis to its cDNA. Previous studies suggested the presence of an activation suppressing sequence in the amino-terminal half of c-raf product. Loss of the sequence by genetic rearrangement was presumed to convert c-raf to possess transforming activity. To identify such sequence, we prepared cDNA mutants by random linker insertion. Synthetic oligonucleotide linker was inserted into the plasmid containing cDNA at a single and random site. Coupling two different mutants, in-frame deletion mutants were constructed systematically. Analysis of these deletion mutants revealed a region, the loss of which made c-raf activated.