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Abstract
A specialized transducing phage for the srlA gene, specifying the sorbitol-specific Enzyme II of the phosphoenolpyruvate: sugar phosphotransferase system, was constructed and its DNA was analysed by restriction endonuclease digestion. Phage construction involved four steps: (1) integration of λ into the srlA gene; (2) selection of phage carrying (a) the left and (b) the right end of the srlA gene by means independent of the function of the new DNA acquired; (3) reconstitution of the srlA gene in a dilysogen of these two phage; and (4) the excision, using the heteroimmune lambdoid phage 21, of a plaque-forming srlA + phage from the dilysogenic chromosome. Comparison of the DNA restriction digests of the transducing phage with those of its parents and of wild-type λ revealed fragments consisting partly of λ and partly of Escherichia coli DNA. The junction points in the intermediate phage define a site that must lie within the reconstituted gene of the final phage. This technique should be of general application in relating genes, cloned by our method, to DNA sequences.
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