<p><b>Copyright information:</b></p><p>Taken from "Down-regulation of human topoisomerase IIα expression correlates with relative amounts of specificity factors Sp1 and Sp3 bound at proximal and distal promoter regions"</p><p>http://www.biomedcentral.com/1471-2199/8/36</p><p>BMC Molecular Biology 2007;8():36-36.</p><p>Published online 20 May 2007</p><p>PMCID:PMC1885802.</p><p></p> (A) High levels of Sp1 and the formation of Sp1 multimers results in increased transcriptional activity of the topoisomerase IIα promoter. (B) A repressive effect on promoter activity when Sp1/3 levels are equal as Sp1 can no longer form protein/protein interactions because of Sp3 occupancy at either GC1 or GC2. (C) Higher Sp3 levels show a dominant repressive effect of promoter activity as most GC1 and GC2 elements are occupied by Sp3
