Analysis of temperature-sensitive functions of Fos: lack of a correlation between transformation and TRE-dependent trans-activation.

We have identified and characterized a mutant v-Fos protein (DN16G) that is temperature sensitive for transformation. This protein contains an asparagine to glycine substitution at position 156 in the basic region encompassing the DNA contact site. This point mutation also strongly decreases trans-activation in a transient expression assay, using the collagenase 12-O-tetradecanoyl phorbol 13-acetate (TPA)-responsive element (TRE) as the target element. However, the apparent correlation between trans-activation and transformation does not hold in view of the observation that under certain temperature conditions (DN16G at 39.5 degrees C and E300 at 37 degrees C) both proteins showed similarly poor transactivation properties, but dramatically differed in their transforming potential. These findings clearly suggest that the activation of transcription via TREs as analysed in this study is not a crucial mechanism in Fos-induced transformation.