A. Record of trans addition of 0.47 µM His-YFP to a membrane containing (PA63F427A)7 channels. After the current (shown as a black line) produced by (PA63F427A)7 channels reached a steady state at −20 mV, His-YFP was added at the green arrow (voltage held at −20 mV), reducing the current by a factor of ~6. The zero baseline of current is shown as a dashed red line. B. Single-channel records of the trans effect of His-YFP on the conductance of membranes containing two (PA63F427A)7 channels (top) and two WT (PA63)7 channels (bottom) at −20 mV. Subsequent unblocking at +20 mV (not shown) confirmed that both channels were still present. The three dashed red lines in each record represent, respectively, the zero baseline of conductance, the open state conductance of one channel, and the open state conductance of two channels. Top record is 170 seconds long and bottom record is 90 seconds long; both are filtered at 10 Hz.