ROLE OF THE TRANSCRIPTIONAL ACTIVATOR APPY IN REGULATION OF THE CYX APPA OPERON OF ESCHERICHIA-COLI BY ANAEROBIOSIS, PHOSPHATE STARVATION, AND GROWTH-PHASE

Transcriptional lacZ fusions have been used to analyze the regulation of the appA operon of Escherichia coli. The appA operon contains the g enes cyxA and cyxB, coding for the putative third cytochrome oxidase, and appA, encoding acid phosphatase. The analysis showed that the cyxA B and the appA genes are cotranscribed from a potentially strong promo ter, p(cyx), located immediately upstream of cyxA and that the operon in addition contains an internal promoter, p(appA), contributing signi ficantly to the transcription of the appA gene. The two prompters were both induced by starvation for P-i and by entry into stationary phase . The cyx promoter was in addition found to be activated by anaerobic growth conditions. The product of the previously identified appY gene, which when present on a high-copy-number plasmid stimulates synthesis of acid phosphatase, was shown to activate the cyx promoter. An inser tion mutation in the appY gene was constructed in vitro and recombined into the chromosome. The appY mutation eliminated induction of the cy x promoter by anaerobiosis and severely reduced induction of this prom oter by phosphate starvation and upon entry into stationary phase but had no effect on induction of the appA promoter. The appY mutation had no effect on survival in stationary phase, nor did it have any effect on growth rate or yield under aerobic or anaerobic conditions. The po ssibility that AppY is a third global regulator of energy metabolism g enes is discussed.