Fig. 1.

Variation in induction parameters of mutant GRs in CV-1 cells with more GR. Triplicate data points ± transiently transfected GR plasmid (Low GR = 0.05 ng/well, High GR = 0.5–1 ng/well) were analyzed to determine the A_max, PAA, and EC₅₀ as described in Materials and Methods (error bars = S.E.M. from 4 independent experiments). P-values for mutant vs. wild type GR under the same conditions are * < 0.05 and ** < 0.005. Under conditions such as the present where very few differences exist between the conditions with different receptors, the prevailing model of steroid hormone action is that the EC₅₀ of gene induction is directly proportional to the affinity of steroid binding to its cognate receptor. Therefore, the predicted EC₅₀ of Dex with the mutant GRs, indicated by the thick horizontal lines, can be calculated by multiplying the EC₅₀ of Dex with wild type GR by the relative increase in the K_d for cell-free Dex binding to the mutant receptors. This relative increase in K_d was previously determined (9) by Scatchard analysis to be 1 for wt GR, 2.8 for Q588K, 5.9 for A625I, and 2.4 for L626I.