Figure 3.

Stepwise deletions in ^CTS3 and the S3–S4 linker. (a) Sequence of ^CTS3 through ^NTS4. (b–g) Currents of mutant channels that lack the entire ^CTS3 and partial S3–S4 linker sequences as indicated. Currents were elicited by stepping membrane voltage from the −100 mV holding potential to between −80 mV and 80 mV in 10 mV increments. Current shown in b, d and e were corrected for background currents with the P/4 protocol. (h) G-V curves of the deletion mutants, along with that of wild-type (Fig. 1b), where the curves are fits of a Boltzmann function, yielding V_1/2 = 6 ± 1.2 mV and Z = 2.5 ± 0.2 (mean ± s.e.m., n = 10) for ΔY323–P341; V_1/2 = 35 ± 0.5 mV and Z = 2.0 ± 0.1 (n = 14) for ΔY323–K342; V_1/2 = 3.0 ± 0.7 mV and Z = 3.5 ± 0.3 (n = 8) for ΔY323–A343; and V_1/2 = 22 ± 0.7 mV and Z = 1.6 ± 0.1 (n = 6) for ΔY323–P344. We calculated conductance values for the G-V curve of ΔY323–K342 from the current and K⁺-driving force ratio, and used the tail current method for the other three mutants.