The colicinogenic factor K has been transferred from E. coli K 235 to Proteus mirabilis. The DNA of the colicinogenic Proteus has been shown to contain a small amount of a satellite DNA which presumably harbors the Col K factor.

In the presence of mitomycin C the colicinogenic Proteus secretes colicin K into the growth medium. The bacteriocin has been purified by chromatography and obtained as an immunologically homogeneous substance unconjugated with other antigens of the Proteus bacillus.

Proteus colicin K is a protein of relatively low molecular weight. It contains all of the usual amino acids except cysteine and is free of lipids and polysaccharides. The bacteriocin can be separated by electrofocusing into two major components. The latter have the same biological properties but differ in their specific electrical charges.

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