TRANSFORMATION OF PRIMARY CHICK-EMBRYO FIBROBLASTS BY VIRALLY-EXPRESSED C-JUN REQUIRES NO MUTATION IN THE PROTEIN WHEN A SUFFICIENT LEVEL OF C-JUN PROTEIN IS REACHED
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- Published online on: January 1, 1994 https://doi.org/10.3892/or.1.1.185
- Pages: 185-190
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Abstract
Proto-oncogene c-jun transforms primary chick embryo fibroblasts as a single gene when expressed from the replication competent retrovirus R (or RCAS). We have investigated whether transformation is caused by accumulating mutations within the proto-oncogene sequence during the retrotranscription process. c-jun coding sequences carried by three independently isolated R-cJUN viruses have been cloned and entirely sequenced. Two of these-were shown to carry no mutation demonstrating that deregulated expression of a normal c-Jun product is sufficient for transformation. On the contrary when expressed from non replicative Rneo vector lacking gag and pol sequences, the avian c-jun no longer transformed. This difference is correlated with weaker c-Jun accumulation in the second case. When expressed from the same Rneo vector, low level of v-Jun or of the heterologous mouse c-Jun still transform. Taken together, these data strongly suggest that a threshold level of c-Jun product is required for transformation and that this critical level can be lowered by mutations in c-jun or by the synthesis of an heterologous protein.