The complete 648 amino acid sequence of the human raf oncogene was deduced from the 2977 nucleotide sequence of a fetal liver cDNA. The cDNA has been used to obtain clones which extend the human c-raf-1 locus by an additional 18.9 kb at the 5' end and contain all the remaining coding exons.

Two human genes homologous to the raf/mil oncogene have been cloned and sequenced. One, c-raf-2, is a processed pseudogene; the other, c-raf-1, contains nine exons homologous to both raf and mil and two additional exons homologous to mil. A 3' portion of c-raf-1 containing six of the seven amino acid differences relative to murine v-raf can substitute for the 3' portion of v-raf in a transformation assay. Sequence homologies between c-raf-1 and Moloney leukemia virus at both ends of v-raf indicate that the viral gene was acquired by homologous recombination. Although the data are consistent with the traditional model of retroviral transduction, they also raise the possibility that the transduction occurred in a double crossover event between proviral DNA and the murine gene.

The complete 606 amino acid sequence of the human A-raf oncogene has been deduced from the 2453 nucleotide sequence of a human T cell cDNA. A cysteine-rich region located near the amino terminus, which is highly conserved in A-raf and c-raf, shows significant homology with protein kinase C. A 5' deleted fragment of the cDNA has been incorporated into a murine retrovirus which endows the virus with the ability to transform cells in vivo and in vitro. Functionally, human A-raf is similar to v-raf and v-mos in that transformation is independent of ras gene function.

We characterized mink cell focus-forming murine leukemia viruses that were isolated from C3H/MCA-5 cells after induction with 5-iododeoxyuridine in culture. Mink lung epithelial cells malignantly transformed in vitro by induced virus were the source of four molecular clones of mink cell focus-forming virus, CI-1, CI-2, CI-3, and CI-4. Three clones, CI-1, CI-2, and CI-3, had full-length mink cell focus-forming viral genomes, one of which (CI-3) was infectious. In addition, we obtained a defective viral genome (CI-4) which had a deletion in the envelope gene. A comparison between the envelope genes of CI-4 and those of spleen focus-forming virus by heteroduplex mapping showed close homology in the substitution region and defined the deletion as being identical to the pl5E deletion of spleen focus-forming virus. The recombinant mink cell focus-forming genomes are not endogenous in C3H/MCA-5 cells and therefore must have been formed in culture after induction by 5-iododeoxyuridine. CI-3, the infectious clone of mink cell focus-forming murine leukemia virus, was dualtropic, and mink cells infected with CI-3 were altered in their response to epidermal growth factor. In the presence of epidermal growth factor at 10 ng/ml, uninfected mink cells retained their epithelial morphology in monolayer culture and did not form colonies in soft agar. In contrast, CI-3 virus-infected mink cells grew with fibroblastic morphology in monolayer culture and showed an increased growth rate in soft agar in the presence of epidermal growth factor.

The recently described acute transforming virus 3611-MSV contains cellular sequences designated v-raf. Mouse cellular DNA contains a single-copy sequence homologous to this oncogene (c-raJ), and Southern blot analysis of hamster-mouse somatic cell hybrid DNAs showed that the mouse c-raf sequence is present on chromosome 6.