Identification of amino acid residues in the ETS transcription factor Erg that mediate Erg-Jun/Fos-DNA ternary complex formation

Jun, Fos, and Ets proteins belong to distinct families of transcription fac tors that target specific DNA elements often found jointly in gene promoter s. Physical and functional interactions between these families play importa nt roles in modulating gene expression. Previous studies have demonstrated a direct interaction between the DNA-binding domains of the two partners. H owever, the molecular details of the interactions have not been investigate d so far. Here we used the known three-dimensional structures of the ETS DN A-binding domain and Jun/Fos heterodimer to model an ETS-Jun/Fos-DNA ternar y complex. Docking procedures suggested that certain ETS domain residues in the DNA recognition helix alpha (3) interact with the N-terminal basic dom ain of Jun. To support the model, different Erg ETS domain mutants were obt ained by deletion or by single amino acid substitutions and were tested for their ability to mediate DNA binding, Erg-Jun/Fos complex formation, and t ranscriptional activation. We identified point mutations that affect both t he DNA binding properties of Erg and its physical interaction with Jun (R36 7K), as well as mutations that essentially prevent transcriptional synergy with the Jun/Fos heterodimer (Y371V), These results provide a framework of the ETS/bZIP interaction linked to the manifestation of functional activity in gene regulation.