Studies of colicin induction with an imm- col+ mutant of the plasmid colicin E1.

Summary A mutant of a derivative of the colicin E1 plasmid has been isolated that does not confer immunity to colicin E1 on its host (imm^-) although it is still capable of producing colicin (col⁺). Cells carrying the col⁺, imm^- plasmid are capable of forming colonies and grow best in liquid culture in the presence of trypsin. The induction of colicin synthesis by ultraviolet light has been analysed using this mutant plasmid. The results suggest that a) the expression of the col⁺ gene may be delayed for many generations after the inducing stimulus, b) although induced cells are usually killed they can reproduce and c) the capacity to produce colicin can be propagated and segregated into the progeny of an induced cell.