A plasmid which naturally occurs in some strains of the bacteria Escherichia coli. It codes for an E. coli-produced antibiotic called a colicin and immunity to its self-produced colicin (so that it doesn't unintentionally destroy itself). It is one of a number of such plasmids, each of which code for a different type of colicin. The plasmid is useful for making cloning vectors for making recombinant DNA molecules.