[Plasmid proteins inhibiting the activity of K and E1 colicins].

Plasmid proteins with m. w. of 14 000--15 000 were chromatographically isolated from lysates of E. coli cells containing plasmids ColK and ColE1. These proteins can reversibly inhibit the killing activity of K and E1 colicine and appear to be the immunity proteins of ColK and ColE1 plasmids and provide the defence of colicinogenic cells from their own colicin. The immunity protein of the ColK plasmid acts both upon K colicin and E1 colicin and vice versa. Unlike E2, E3 colicins or CloDF13 cloacin, K and E1 colicins are extracted from cells in a free state and not in a complex with the immunity protein.