= Colicin E1
{c}
<Colicin E1> is a pore-forming <bacteriocin>, a bacterial <protein> capable of disrupting susceptible bacterial <cell membranes>. Its channel-forming region lies toward the <C-terminus>. The <protein> is distinct from the <Colicin E1 plasmid>, the <DNA> element associated with its production.
A 1983 experiment compared intact <Colicin E1> with its roughly $20\,\mathrm{kDa}$ terminal fragment in artificial planar <lipid bilayers>. Both produced similar individual-channel and aggregate electrical behaviour, supporting localization of channel-forming function to that part of the <protein>.<Comparison of the macroscopic and single channel conductance properties of colicin E1 and its COOH-terminal tryptic peptide by J. O. Bullock and others>[Abstract; intact protein versus C-terminal fragment]{ref}
Both forms could associate with a <lipid bilayer> without an applied <electric potential difference>, while formation of conducting channels required the specified polarity of <membrane potential>. Attachment and channel opening are therefore distinguishable steps: seeing membrane-associated <protein> does not establish that an ion-conducting pore is open.<Comparison of the macroscopic and single channel conductance properties of colicin E1 and its COOH-terminal tryptic peptide by J. O. Bullock and others>[Abstract; membrane association versus potential-dependent conduction]{ref}
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