Strains with lac fused to each of the arylsulfatase (ats) and tyramine oxidase (tyn) opérons in Escherichia coli were isolated. Synthesis of j3-galactosidase in strains with tyn:: lac fusions was induced by tyramine, histamine, tryptamine, dopamine and octopamine, and the induction of the tyn operon was subject to catabolite and ammonium repressions. These repressions were relieved when the cells were grown with a poor carbon or nitrogen source. No arylsulfatase activity is detected in E. coli strains. Synthesis of jff-galactosidase in strains with ats:: lac fusions was repressed by sulfur compounds. The repression was relieved by monoamine compounds, which induced tyramine oxidase synthesis. The inhibition of tyramine oxidase activity by cysteine resulted in a decrease of the derepressed synthesis of jS-galactosidase in the ats:: lac fusion. Repressing and derepressing conditions for the tyn operon prevented and stimulated, respectively, expression of the ats operon. Thus, the expression of latent arylsulfatase in E. coli seems to be regulated by expression of the tyn operon.
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