The structural requirements of raf and myc oncogenes were determined for transformation, synergism, growth factor abrogation, transforming growth factor induction, and autoregulation of cellular myc genes. The minimal transforming sequences of different members of raf family genes (v-raf, c-raf, mouse and human A-raf) were determined in established fibroblast cell lines and in newborn mice by making a series of raf transducing murine retroviruses with various N and C terminal deletions. Furthermore, a series of v-myc recombinant murine retroviruses were constructed with various deletions in v-myc. We found that a deletion of 14 amino acids from the C-terminal of v-raf did not affect its transforming activity, wheras deletions of 27 and 28 or more amino acids from the C-terminus of A-raf and v-raf, respectively, abolished their transforming activity. Our results, and previous relults from our lab, indicate that amino terminal truncation is involved in the ocogenic activation of raf family genes, since all the natural transforming versions of the raf genes are amino terminally truncated. To further define this region, we are constructing raf recombinant retroviruses with various deletions in the amino terminal half of c-raf and A-raf genes. All deletions that were made in the kinase domain of A-raf abolished its transforming activity indicating that this activity is absolutely required for transformation. Preliminary results of the v-myc recombinant retroviruses demonstrated a region of about 100 amino acids in the center of the gene, which is absolutely required for the negative regulation of v-myc on the expression of c-myc.
