The purification, structure and synthesis of proticine 3.

The ability of Proteus mirabilis to produce the bacteriocin, proticine 3, is found almost exclusively in strains that cause severe infections of the upper urinary tract. Proticine 3 was purified from lysates of mitomycin C-induced cultures. Biological activity was associated with structures resembling bacteriophage tails which, when first produced, were in the form of "nails" with one pointed end and a base plate with appendages at the other end. This form was unstable and changed to a "rocket" form in which the outer sheath contracted and thickened to reveal a protruding, hollow core that often became detached from the sheath. Purified proticine 3 comprises two major and nine minor proteins. Fluorography showed that during production of the proticine, a 58,000 mol. wt protein was synthesized late in the induction process and became the most intensely labelled protein in the culture. Synthesis of this protein coincided with the appearance and increase in titre of biologically-active proticine within the cell and with the appearance of "nail" forms. The protein is believed to be shed when an active "nail" is converted to an inactive "rocket" and to be either the component of proticine 3 associated with its lethal activity, or the protein required for the correct assembly of the constituent components into a biologically-active particle. The role of proticine 3 as a virulence factor is discussed.