Lysis of Escherichia coli by Cloned X174 Gene E Depends on its Expression

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Abstract
The lysis gene E of bacteriophage ϕX174 was cloned under transcriptional control of the lefthanded lambda promoter, giving rise to plasmid pSB12. Plasmid pSB22, identical to pSB12 except for an amber mutation in gene E, was constructed in the same way. Induction of the cloned wild-type gene by heat inactivation of the thermosensitive λ cI857 repressor resulted in lysis of the host bacteria. With plasmid pSB22 only amber suppressor strains of Escherichia coli lysed after heat inactivation of λ cI857. Lysis of E. coli was shown to depend on the rate of gene E translation and on the growth phase of the bacteria. Stationary cells could not be lysed by the gene E product (gpE), even if present in sufficient amounts to lyse growing cells. By isotopic labelling gpE could be detected among the proteins synthesized in normal E. coli as well as in minicells. Determination of gene E expression suggested that gpE synthesis is translationally regulated.