Effects of nucleosides on repression of .BETA.-galactosidase synthesis by glucose and by glycerol in Escherichia coli K12.

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Ribonucleosides (inosine, adenosine, guanosine, cytidine, and uridine) or deoxyribonucleosides (deoxyadenosine, deoxyguanosine, deoxycytidine, deoxyuridine, and thymidine) themselves did not repress β-galactosidase formation in Escherichia coli K12 strain 3000 and other derivative strains but all these nucleosides except guanosine and deoxyguanosine enhanced the repression by glucose or glycerol. Adenosine 3', 5'-cyclic monophosphate reversed the effects of glucose, and of glucose (or glycerol) plus adenosine or cytidine on β-galactosidase synthesis. Neither ribose, deoxyribose nor any of the nucleic acid bases tested except hypoxanthine and adenine repressed the synthesis of β-galactosidase or enhanced the repression by glucose or glycerol. The effects of the nucleosides were dependent on their concentrations and, in the presence of 25mM glucose or glycerol, adenosine and cytidine caused maximal repression at concentrations of 0.2mM or more. Adenosine (0.4mM) exerted its maximal effect in the presence of the concentration of glucose or glycerol which alone caused maximal repression (0.5mM glucose or 0.37mM glycerol). In the absence of inducer, adenosine (0.4mM) also enhanced the effect of glucose on β-galactosidase synthesis in I- constitutive strains.
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