Expression of a gene in a 400-base-pair fragment of colicin plasmid ColE2-P9 is sufficient to cause host cell lysis

Abstract

The colicin E2 immunity (ceiB) and lysis (celB) genes of colicin plasmid ColE2-P9 were cloned as a 900-base-pair insert controlled by the lac promoter in plasmid pUR222. Hosts [Escherichia coli] carrying this plasmid were immune to colicin E2, produced increased amounts of immunity protein (MW, 9000) and 2 smaller proteins (MW 5000 and 3000) and lysed when incubated in medium containing isopropyl-.beta.-D-thiogalactopyranoside (IPTG). A 400-base-pair lacp-distal fragment derived from the insert in this plasmid was recloned in the same orientation into pUR222. Although hosts carrying this plasmid also lysed when grown in the presence of IPTG, they were sensitive to colicin E2 and produced increased amounts of the 5000 and 3000 MW proteins when treated with IPTG. Evidently, expression of celB (production of the 5000 and 3000 MW proteins) can cause host cell lysis in the absence of colicin production and derepression of the host cell SOS system.