Oncogenic activation of murine mos protein kinase by DNA rearrangement of its N-terminal coding region.

An activated c-mos oncogene was detected by DNA transfection assay of hamster SHOK cells with DNAs from X-ray-induced mouse osteosarcoma. It was molecularly cloned by the cosmid rescue method and found to form transformed foci of SHOK cells. Genomic DNA sequencing revealed that in this oncogene the N-terminal coding region of the mouse proto-mos gene was deleted and replaced by a hamster-derived sequence in the primary transformant, suggesting that activation was due to the rearrangement during transfection. The gene product was about 37 kDa and was immunoprecipitated with anti-mos antibody from a lysate of a SHOK cell transfectant. This truncated mos (t-mos) gene transformed SHOK cells more effectively than v-mos. A chimeric gene construct of this hamster-derived upstream sequence and normal mouse c-mos also transformed SHOK cells at a lower level, whereas neither t-mos nor the chimeric c-mos gene transformed NIH3T3 cells appreciably. The high transforming efficiency of t-mos in SHOK cells was due not only to truncation of the coding region but also to its integration under a putative promoter sequence derived from the hamster genome. This is the first report of detection of an activated c-mos gene by DNA transfection assay.