FIG. 1.
Cloning of the gus operon. A 7,740-bp PstI-HindIII fragment containing the gus operon from a natural E. coli fecal isolate (CE1) was cloned into the PstI and HindIII restriction sites (not shown) of low-copy-number plasmid pLAFR3, generating plasmid pKW219. The corresponding fragment of the gus operon from E. coli K-12 was also cloned to generate plasmid pKW220 (not shown). A BstYI fragment (3,368 bp) containing the gusBCCE1 genes was subcloned into plasmid pAD284 at the HpaI site, generating plasmid pWJL4, so that the gene expression is under the control of the λ OLPL promoter. Plasmids containing the gusBCE1 gene (pWJL6) and the gusCCE1 gene (pWJL11) were generated from plasmid pWJL4 by a combination of restriction digestions (see Materials and Methods for details). The base pair numbers are those listed in GenBank (accession number M14641), while the base pair numbers in brackets correspond to those listed in the genome sequence of E. coli MG1655 (3).