Figure 5.

Simultaneous deletions in S3b and ^NTS4. (A) Sequences of S3b through ^NTS4. The lines under the upper sequence indicate the pair of hextuplet residues simultaneously deleted from S3b and ^NTS4 (construct #1); the line under the lower sequence indicates the 43 residue sequence replaced by a glycine triplet (construct #2). (B) Currents of channel construct #1 described in panel A. (C) Currents of channel construct #2 in panel A. (D) Currents of mutant channels similar to those in panel C, except that R3 is also deleted. (E) Currents of mutant channels containing three mutations (R1M, R2Q and R3N). Currents in panels B and C were elicited with the protocol shown in Fig 2B, whereas for panels D and E, the test pulses ranged from −100 mV to 60 mV (D) or to 30 mV (E). They were recorded in the presence of 20 mM Rb⁺ (B, C) or 100 mM Rb⁺ (D, E) in the bath solution. (F) Normalized tail currents (mean ± s.e.m.) plotted against membrane voltage. The curves through the data for the mutant shown in panels B and C are Boltzmann fits, yielding V_1/2 (in mV) of −23 ± 0.3 (B) and −18 ± 0.3 (C), and Z of 1.7 ± 0.1 (B) and 2.1 ± 0.1 (C). The wild-type G-V curve (open symbols), taken from Fig. 2H, is re-plotted for comparison. All data shown are mean ± s.e.m. (n = 5–30).