Polyamine Stimulation of arcA Expression in Escherichia coli

The effects of two natural polyamines (putrescine and spermidine) on the synthesis of ArcA, a response regulatorof the Arc two-component signal transduction system, were studied using an E. coli mutant deficientin polyamine biosynthesis. Endogenous polyamine deficiency of the mutant resulted in markedreduction in the ArcA level determined by Western blot analysis. Putrescine supplement to the growthmedium effectively increased the ArcA level of the mutant in a concentration-dependent manner. Spermidinealso stimulated the ArcA level in the mutant to a greater degree than putrescine. Expressionof arcA'::lacZ operon fusion in the mutant was stimulated 6-fold and 10-fold by putrescine and spermidineat a 1mM concentration, respectively, indicating that the stimulatory effect of the polyamineson ArcA synthesis is due to transcriptional induction, and that spermidine is a more potent arcAinducer than putrescine. The polyamine-dependent arcA'::lacZ induction was growth-phase-dependentand independent of either arcA or fnr which are two regulators involved in anaerobic stimulation ofthe ArcA level. These results suggested that putrescine and spermidine polyamines may be potentialintracellular signal molecules in the control of arcA expression, and thereby may play an important rolein cellular metabolism. The effects of two natural polyamines (putrescine and spermidine) on the synthesis of ArcA, a response regulator of the Arc two-component signal transduction system, were studied using an E. coli mutant deficient in polyamine biosynthesis. Endogenous polyamine deficiency of the mutant resulted in marked reduction in the ArcA level determined by Western blot analysis. Putrescine supplement to the growth medium effectively increased the ArcA level of the mutant in a concentration-dependent manner. Spermidine also stimulated the ArcA level in the mutant to a greater degree than putrescine. Expression of arcA'::lacZ operon fusion in the mutant was stimulated 6-fold and 10-fold by putrescine and spermidine at a 1mM concentration, respectively, indicating that the stimulatory effect of the polyamines on ArcA synthesis is due to transcriptional induction, and that spermidine is a more potent arcA inducer than putrescine. The polyamine-dependent arcA'::lacZ induction was growth-phase-dependent and independent of either arcA or fnr which are two regulators involved in anaerobic stimulation of the ArcA level. These results suggested that putrescine and spermidine polyamines m