Human KCNQ1 mutants confirm that Gly272, Val324, and Val334 of KCNQ1 are important for KCNE1 modulation. (A) V_1/2 values without (light gray bars) and with (dark gray bars) KCNE1 for hKCNQ1 (hQ1) point mutants are plotted. Asterisks indicate the significant reduction in the level of V_1/2 with KCNE1 compared with that of hKCNQ1 with KCNE1 (Dunnett’s test). (B) Representative current traces for hKCNQ1 G272A/V334I double mutant in the absence (left) and presence (right) of KCNE1. The membrane potential was stepped up from −100 to +60 mV in 20-mV increments. (C) G-V relationships for the hQ1 G272A/V334I mutant in the absence (open circles) and presence (closed red circles) of KCNE1. The G-V relationships of WT hKCNQ1 in the absence (black dotted curve) and presence (red dotted curve) of KCNE1 are superimposed.