Summary: Gene fusions between the structural genes and various genes of the hexuronate system of K12 were isolated by the technique of Casadaban. Mud(Ap ) and λp-Mu insertion mutants were constructed in which the genes were fused to the regulatory region of the uxu operon. In all the fusion strains, β-galactosidase expression was shown to be inducible by the natural inducers of the operon (glucuronate and fructuronate) and sensitive to catabolite repression by glucose. In addition we isolated a Mud(Ap ) fusion where the genes were fused to the regulatory gene. In this fusion the synthesis of β-galactosidase reflects the regulation of the gene. In the presence of a wild-type allele, partial repression of β-galactosidase expression was found; the repression was removed when inducer was added. This result indicates that while the gene is subject to autogenous control, the repressor may have only a low affinity for its own operator.


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