FIGURE 2.

Schematic of a single-channel record obtained from a bilayer treated with the channel-forming portion of colicin Ia. The channel initially opens to the same conductance as that obtained with whole colicin Ia; the topography corresponding to this state has four transmembrane segments, with H1 being one of these segments. (Compare this diagram with that for whole colicin Ia in Fig. 1.) The conductance subsequently drops to a lower conductance; the topography corresponding to this state has three transmembrane segments, with H1 having been translocated to the trans side. H1 and H2-5 refer to α-helices in the water-soluble form of colicin Ia; they are not necessarily α-helices in the channel state of this protein.