Mechanism of G1 Radiation Checkpoint Activation Figure 5. Effect of target knockdown on radiation survival. A–I) Target knockdown affects survival of IR exposed cells. HCT116 cells transfected with target siRNA alone or in combination with siRNA targeting CHK1. Cells were Mock-irradiated or irradiated with 2 Gy or 5 Gy and viable cells quantified 5 days later. Data plotted are normalized to the respective untreated controls. Filled squares = combined target and CHK1 knockdown (Target/CHK1), open squares = CHK1 only (Li/CHK1), filled triangles = Target only (Target/NT), open triangles = Mock (Li/NT). Error bars represent the variance from the mean from three technical replicates. K) Modulation of RB1 phosphorylation by target knockdown. Parallel PLoS ONE | www.plosone.org 8 February 2012 | Volume 7 | Issue 2 | e31627