Construction and characterization of E. coli promoter-probe plasmid vectors I. Cloning of promoter-containing DNA fragments

Derivatives of the Escherichia coli drug-resistance plasmid pBR316 have been constructed which act as molecular probes for promoter-containing DNA restriction fragments from various prokaryotic genomes. The plasmids, designated pBRH1 and pBRH3B, contain a unique EcoRI restriction site located within the promoter for the tetracycline resistance (Tc^r) gene. This site was created by the insertion of a chemically synthesized octanucleotide, containing the EcoRI cleavage sequence, into the HindIII site of pBR316. Base-pair alterations within the Tc promoter produced by this insertion resulted in a substantial reduction (pBRH3B) or elimination (pBRH1) in ability of these plasmids to confer Tc resistance to the host strain. Cloning of EcoRI-cleaved foreign DNA fragments into the EcoRI site of these plasmids allows for the isolation of recombinant transformants with Tc^r levels greater than that of the plasmid vector. Further characterization of these recombinant plasmids demonstrates that the Tc^r phenotype is dependent upon the orientation of the inserted fragment, but not on the molecular weight. We have concluded that these fragments carry promoters which, in the proper orientation, allow for the transcription of the Tc^r gene. The utility of these "promoter-probe" plasmids lies in the ability to select for promoter-containing DNA fragments by insertional activation of the Tc^r gene.