Identification and restriction endonuclease mapping of the threonine operon regulatory region.

A DNA fragment carrying the thrP region of Escherichia coli has been identified and characterized. Starting from a secondary site lysogen of bacteriophage λ, where the position of the prophage is either within thrP or between thrP and thrP structural genes (Gardner et al., 1974; Gardner &; Smith, 1975) it has been possible to isolate transducing phages which carry bacterial DNA from either side of the prophage. By Int-Xis mediated site-specific recombination we have generated recombinant transducing phages which carry an intact thrP region. A phage carrying a regulatory mutation, which maps in the thrP region, has also been constructed.Mapping with several restriction endonucleases has allowed us to construct a map of the cleavage sites of the thrP region. A 1700 base-pair HaeIII fragment carrying the secondary attachment site (attΔOΔ′) was isolated and its position was localized within a 180 base-pair TaqI-HhaI restriction fragment. The location of attΔOΔ′ in the HaeIII fragment suggests that the entire thrP region is carried by this fragment.