Summary of MTSET effects on the macroscopic current through colicin Ia cysteine mutant channels and wild-type. (A) Trans MTSET. (B) Cis MTSET. For mutants showing a response to MTSET, each bar represents the percent change in current (mean ± SD). At least three experiments were performed for each condition. For mutants G593C and S594C with trans MTSET, the error bars were truncated so that the data for the other mutants could be displayed more clearly. The bars are color-coded as follows: red, has a single-channel MTS effect; blue, no MTS effect after cis perfusion. Of the remaining (gray) bars, the effect of cis MTSET on Y601C was not observed consistently (as reflected in the large standard deviation) and hence was not considered to be a real effect. Cis MTSET had a very slow effect on G602C, as described in the text, but an effect on single channels was not demonstrated. The lines on the left indicate the limits of helices H8 and H9, as defined by the crystal structure. Solutions were as in Fig. 1.