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A bacteriocin is an antimicrobial peptide or protein produced by bacteria that acts against susceptible bacterial strains. The category describes a biological product and its antibacterial action; susceptibility depends on both the product and the target.^[ref]

Colicin E1 supplies a concrete mechanistic example. An experiment compared the complete protein with its C-terminus fragment in artificial lipid bilayers. Similar channel properties in the two forms localized pore-forming activity to that region. Membrane association could occur without the membrane potential needed for conducting channels to form.^[ref]

The experiment shows how to separate delivery, attachment and action of a bacterial product. It establishes a channel mechanism for the tested Colicin E1 system; the class name bacteriocin does not assign that same mechanism to every member. A growth-inhibition observation alone would not identify which molecular step caused the inhibition.

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.^[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.^[ref]