Fusion of the lac Genes to the Proximal Promoters of the deo Operon of Escherichia coli K12

SUMMARY: Fusions of the lac structural genes to the proximal promoters deoP and cytP of the deo operon have been isolated using a λ (lac, Mu') phage. This phage was inserted into a heat-inducible Mu prophage which had itself been inserted into the deoA gene. Selection was made for heat-resistant derivatives of this lysogen which maximally expressed the lac genes when an inducer of the deo operon was present; these were shown to have the lac genes fused to the deo operon - in some cases with a concomitant deletion of the deoC gene, whilst in others deoC was retained. The level of β-galactosidase activity in these strains was induced by growth in the presence of deoxyadenosine or cytidine, both of which lead to induction of the deo enzymes - deoxyadenosine through the deoOP system and cytidine through the cytOP system. The level of induction of β-galactosidase was of the same order as the level of induction of deoxyriboaldolase, the deoC gene product, in those strains retaining an intact deoC + gene. Plaque-forming λ phages carrying the deo-lac fusions were isolated by inducing the lysogens with mitomycin C.