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Oncogenes of the ras family stimulate DNA synthesis when microinjected into quiescent mouse and hamster fibroblasts, as detected by in situ autoradiography. The molecularly cloned genomes of Harvey and Kirsten sarcoma viruses, the cloned Harvey ras gene, and the product of the v-ras gene, the p21v-rasH protein, stimulate DNA synthesis in quiescent cells. This stimulation is comparable to the stimulatory activity of the microinjected SV40 T-antigen-coding gene. The demonstration that these oncogenes can stimulate transient DNA synthesis in quiescent cells is relevant to understanding the mechanism by which these genes are able to transform cells in vitro and induce tumors in animals.

The 50-70 S RNA complex of a clone of Kirsten murine leukemia virus (Ki-MLV), propagated in NIH 3T3 cells, as well as that of a Moloney (Mo)-MLV, propagated in a mouse thymus-bone marrow cell line, contained an approximately 30 S RNA of unknown biological activity in addition to 38 S genomic RNA. The approximately 30 S RNA shares with 38 S virion RNA the ability to form 50-70 S RNA complexes and to be packaged by virus particles. The morphology of the cell lines propagating these viruses was indistinguishable from that of uninfected controls.