Construction and Characterization of guaB-lacZ Fusions in Escherichia coli K12

GuaB-lacZ fusion strains of Escherichia coli K12 have been constructed using the Casadaban (1976) gene-fusion technique. The major modification to the procedure was the removal of the guanine requirement of Mu-induced guaA auxotrophs by introduction of a ColEl-gua + plasmid prior to selection of the fusion. Conversion to prototrophy was necessary to overcome problems associated with repression of the gua operon by guanine added to selection media. Induction of the lysogenic fusion strains yielded plaque-forming λ transducing phages that carried the lac genes and either the complete guaB gene and the gua promoter or only a distal portion of guaB.