CtBP-independent repression in the Drosophila embryo. Author Yutaka Nibu, Kate Senger, Michael Levine Publication Year 2003 Type Journal Article Abstract There are three mechanisms of transcriptional repression in eukaryotes. The first is quenching, whereby repressors and activators co-occupy closely linked sites and then the repressor inhibits adjacent activators. The second is direct repression, in which repressors block the function of the core transcription complex. The third is competition, in which repressors compete with activators for a common DNA-binding site. Previous studies have shown that the Drosophila melanogaster CtBP corepressor (dCtBP) is essential for the quenching activity of three short-range sequence-specific repressors in the early Drosophila embryo: Krüppel, Knirps, and Snail. Here we demonstrate that dCtBP is dispensable for target enhancers that contain overlapping activator and repressor binding sites. However, it is essential when Krüppel and Knirps repressor sites do not overlap activator sites but are instead located adjacent to either activators or the core promoter. These findings provide evidence that competition is distinct from quenching and direct repression. Quenching and direct repression depend on dCtBP, whereas competition does not. Keywords Animals, Drosophila Proteins, Gene Expression Regulation, Developmental, Genes, Regulator, In Situ Hybridization, Genes, Reporter, Drosophila melanogaster, Transcription Factors, Recombinant Fusion Proteins, Binding Sites, DNA-Binding Proteins, Protein Binding, Repressor Proteins, Nuclear Proteins, Phosphoproteins, Animals, Genetically Modified, Protein Structure, Tertiary, Kruppel-Like Transcription Factors, Alcohol Oxidoreductases Journal Mol Cell Biol Volume 23 Issue 11 Pages 3990-9 Date Published 06/2003 Alternate Journal Mol. Cell. Biol. Google ScholarBibTeXEndNote X3 XML