Subdomains of p66 can act as dominant negative suppressors of proliferation in clonogenic assays. Clonogenic assays were carried out to assess the effect of various p66 constructs on colony formation in U2OS cells; see the Methods section for details. Cells were plated at densities of 5 × 104 (left hand side) and 2.5 × 104 per well (right hand side) prior to transfection with EGFP constructs and grown under selective conditions for 10 to 20 days before being fixed and stained with Giemsa. The figure shows a representative result. Panel A: pEGFP; panel B: pEGFP-p66; panel C: pEGFP-p66Δ11; panel D: pEGFP-p66S2; panel E: pEGFP-p66NLS.