Figure 6: Simplified scheme of a model promoter regulating MYC and CCND1 transcription (+ other genes at the G1-S restriction point). The model promoter consists of five Transcription Factor Binding Sites - TFBSs, depicted in arbitrary order. TFBSTCF7L2, TCF7L2 binding site; TFBSSMAD4, SMAD4 binding site; TFBSAP1, AP1 binding site; TFBSTP53, TP53 binding site; TFBSE2F-DP1, E2F-DP1 binding site. A. Schematic representation of the promoter with activators (above) and repressors (below) that are assumed to bind to each TFBS in the model. Arrows indicate the potential for binding at the TFBS. The DNA binding regions of the activators (white) and repressors (black) are also shown. B. Equivalent to A, where names of the activator (white) and repressor (grey) TF forms have been replaced by corresponding model variables. x1, β-Catenin-TCF7L2; x1p, pβ-Catenin(Y654)-TCF7L2; x2, SMAD4-TCF7L2; y1, GROUCHO-TCF7L2; y2, pSMAD2(S467)-SMAD4; y3, pSMAD3(S425)-SMAD4; x3, AP1; x3p, pAP1; y4, TP53; x4, E2F-DP1; y5, E2F-DP1-RB. Reproduced from [12], with permission of 2008-2015 Impact Journals, LLC.