Multiple regions of v-Fos protein involved in the activation of AP1-dependent transcription: is trans-activation crucial for transformation?

We show that trans-activation by v-Fos requires several functionally separable regions, including the leucine repeat, the basic DNA-binding region, a directly adjacent acidic cluster, and additional flanking sequences. Structural alterations in the flanking regions are in part responsible for the greater trans-activating potential of the fos gene product of the Finkel-Biskis-Reilly mouse osteosarcoma virus, FBR-MuSV. A point mutation in the acidic cluster, which is known to activate the immortalizing potential of Fos, leads to a significant increase in trans-activation. However, comparison of the trans-activating and transforming properties of mutant Fos proteins suggests that functions other than trans-activation are involved in the induction of transformation.