Fig. 1. Primary selection and secondary quantification of the readthrough effect of the positive hits. ( A ) A schematic of the reporter system used is presented with the R213X sequence. Positive hits were selected according to the fold change in  Metridia -luciferase activity between treatment (at 50 μM) and the median value for the negative controls (untreated cells). The molecules from the Chembridge chemotherapy library and those of the Prestwick library are represented in the left and right panels, respectively. The red crosses correspond to the 465 molecules inducing at least a 1.4-fold increase in activity. ( B ) The dual reporter system is illustrated in the top panel. The red stop indicates the R213X sequence inserted between  lacZ  and  F-luc . The ability of the 43 retained molecules to stimulate readthrough is illustrated in the lower panel. NIH 3T3 cells were treated for 24 h with gentamicin (2.5 mM) as a control or with one of the 43 molecules selected (50 μM) from the Prestwick chemical library (green bars) or the Chembridge chemical library (blue bars). The red asterisks represent the 4 molecules selected for further characterization.