An aqueous channel for filamentous phage export

Filamentous phage f1 exits its Escherichia coli host without killing the ba cterial cell. It has been proposed that f1 is secreted through the outer me mbrane via a phage-encoded channel protein, pIV. A functional pIV mutant wa s isolated that allowed E. coli to grow on large maltodextrins and rendered E. coli sensitive to large hydrophilic antibiotics that normally do not pe netrate the outer membrane. In planar lipid bilayers, both mutant and wild- type pIV formed highly conductive channels with similar permeability charac teristics but different gating properties: the probability of the wild-type channel being open was much less than that of the mutant channel. The high conductivity of pIV channels suggests a large-diameter pore, thus implicat ing pIV as the outer membrane phage-conducting channel.