Characterization of a protein binding site involved in the regulation of transcription elongation within the murine c-myc gene

The c-myc gene was previously shown to be regulated by a conditional block to transcription elongation and sequences from its promoter were implicated in this regulation. The objective of this project was to define the promoter elements involved in the control of transcription elongation. Using heterologous promoter constructs, the ME1a1 protein binding site located in the c-myc promoter was shown to be required for the block to transcription elongation. From mutation analysis, a correlation was established between the binding of nuclear factors to ME1a1 sites in vitro and the ability of these sites to confer block to transcription elongation in vivo, strongly implicating trans-acting factors in this process. Fractionation studies demonstrated that three nuclear factors interact with the ME1a1 site, thus generating three protein-DNA complexes termed "a", "b", and "c". These factors were characterized and a cDNA encoding the protein responsible for complex "c" was isolated. This protein was shown to represent the human homologue of the Drosophila Cut homeodomain protein (hu-Cut) and to repress expression from the c-myc promoter in transient transfection assays