Effect of Purine Limitation Caused by an Amidophosphoribosyl Transferase (purF) Mutation on Polyphosphate Kinase 1 (ppk1) Gene Expression

Abstract

Polyphosphate kinase (ppk) synthesizes polyphosphate (polyP(n+1)) from polyP(n) and ATP and also catalyses its reversal reaction. In the process of identifying stimuli that affect E. coli ppk transcription, we show that purine limitation activates the E. coli ppk promoter by using a single-copy E. coli ppk promoter-lacZ (ppkP(Ec)-lacZ) fusion and Ez-Tn5 random mutagenesis. The ppkP(Ec)-lacZ expression was greatly induced (seven to eleven fold higher depending on the media) in purF mutant cells (e.g. cvpA::Ez-Tn5 and Delta purF mutants). This behavior seems to result from the purine starvation because the ppkP(Ec)-lacZ expression in the purF mutant cells was recovered to the level of wild-type cells by the addition of any type of purines (adenine, guanine, adenosine, and guanosine). The ppkP(Ec)-lacZ expression was also increased in other pur mutants but not as much as in the purF mutant cells. Interestingly, the ppkP(Ec)-lacZ expression was not changed in mutants with defective pyrimidine specific genes (e. g. Delta pyrE and Delta thiC). Transcription of four other bacterial ppk promoters also increased in the purF mutant cells. This data imply that purine deficiency seems to be a common and good inducer in bacterial ppk gene expression. Here, we present a novel report about the effect of purine biosynthesis on ppk gene expression in bacteria.