DNA binding by the ETS-domain transcription factor PEA3 is regulated by intramolecular and intermolecular protein protein interactions

The control of DNA binding by eukaryotic transcription factors represents a n important regulatory mechanism. Many transcription factors are controlled by cis-acting autoinhibitory modules that are thought to act by blocking p romiscuous DNA binding in the absence of appropriate regulatory cues. Here, we have investigated the determinants and regulation of the autoinhibitory mechanism employed by the ETS-domain transcription factor, PEA3. DNA bindi ng is inhibited by a module composed of a combination of two short motifs l ocated on either side of the ETS DNA-binding domain. A second type of prote in, Ids, can act in trans to mimic the effect of these cia-acting inhibitor y motifs and reduce DNA binding by PEA3. By using a one-hybrid screen, we i dentified the basic helix-loop-helix-leucine zipper transcription factor US F-1 as an interaction partner for PEA3. PEA3 and USF-1 form DNA complexes i n a cooperative manner. Moreover, the formation of ternary PEA3 USF-1 DNA c omplexes requires parts of the same motifs in PEA3 that form the autoinhibi tory module. Thus the binding of USF-1 to PEA3 acts as a switch that modifi es the autoinhibitory motifs in PEA3 to first relieve their inhibitory acti on, and second, promote ternary nucleoprotein complex assembly.