DIFFERENTIAL REGULATION OF C-JUN AND JUND BY UBIQUITIN-DEPENDENT PROTEIN-DEGRADATION

c-Jun and JunD are two closely related members of the Jun family of tr anscription factors which markedly differ in their biological function s. Whereas c-Jun behaves as a positive regulator of cell growth and ma y cause cell transformation when overexpressed, JunD antagonizes both of these effects. To better understand how the activities of c-Jun and JunD are controlled, we investigated how their stabilities within the cell are determined. We show that, in contrast to c-Jun which is degr aded following multi ubiquitination, JunD is not efficiently ubiquitin ated and exhibits a correspondingly longer half-life. Mutational analy sis reveals that the determinant for the difference in ubiquitination resides in the NH2-terminal regions of the proteins which in c-Jun con tains the delta-domain.