| Opposite responses of Id 1 to TGFbeta and the related factor BMP are dictated by the specific ability of the TGFbeta mediator , Smad 3 , to activate expression of stress response factor ATF 3 and then recruit this factor to the Id 1 promoter . ^^^ Thus , a Smad 3 mediated primary gene response , ATF 3 induction , enables Smad 3 to participate in an ATF 3 mediated , secondary gene response . ^^^ |