Identification and physical characterization of a Col E1 hybrid plasmid containing a catalase gene of Escherichia coli

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Abstract
A hybrid Escherichia coli: Col E1 plasmid, pLC36-19, containing a catalase gene has been identified in the Clarke and Carbon colony bank. Catalase activity was amplified two- to three-fold in the pLC36-19-containing strain relative to other hybrid-plasmid-containing strains and this activity could be induced three- or four-fold by hydrogen peroxide or ascorbic acid. The plasmid was transferred to a strain chromosomally deficient in catalase synthesis, resulting in a strain with high and inducible levels of catalase. The plasmid was also transferred to a minicell-producing strain and minicells harbouring the plasmid were found to synthesize a labelled protein with a molecular weight of 84 000 characteristic of catalase from E. coli. A catalase activity was also synthesized by the plasmid-containing minicells. Two catalase activities with associated peroxidase activities coded for by the plasmid were separable by polyacrylamide gel electrophoresis and migrated coincident with chromosomally encoded catalase–peroxidase activities. A third catalase activity which did not have an associated peroxidase activity was not coded for by the plasmid. A physical map of the 25.5-kilobase pair plasmid was constructed by restriction nuclease analysis and the relative positions of 38 restriction sites were defined.