SUMMARY: Fusions of the structural genes to the proximal promoters and of the 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 gene. Selection was made for heat-resistant derivatives of this lysogen which maximally expressed the genes when an inducer of the operon was present; these were shown to have the genes fused to the operon - in some cases with a concomitant deletion of the gene, whilst in others 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 enzymes - deoxyadenosine through the system and cytidine through the system. The level of induction of β-galactosidase was of the same order as the level of induction of deoxyriboaldolase, the gene product, in those strains retaining an intact gene. Plaque-forming λ phages carrying the fusions were isolated by inducing the lysogens with mitomycin C.


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