Dual regulation of the ugp operon by phosphate and carbon starvation at two interspaced promoters

Abstract

The ugp operon of Escherichia coli includes genes involved in the uptake of sn-glycerol-3-phosphate and glycerophosphoryl diesters and belongs to the pho regulon which is induced by phosphate limitation. This operon has two transcriptional initiation sites, as determined by SI nuclease mapping of the in vivo transcripts. The downstream promoter has multiple copies of the pho box, the consensus sequence shared by the pho promoters; the upstream promoter has a consensus sequence for the promoters regulated by cyclic AMP and its receptor protein, CRP. PhoB protein, which is the transcriptional activator for the pho regulon, protected the regulatory region with the pho boxes in DNase I footprinting experiments and activated transcription from the downstream promoter in vitro. Studies with transcriptional fusions between ugp and a promoterless gene for chloramphenicol acetyltransferase show that the upstream promoter is induced by carbon starvation in a manner that required the cya and crp genes. PhoB protein may act as a repressor for this upstream promoter, which also overlaps the upstream third pho box. The downstream promoter was induced by phosphate starvation and requires the PhoB protein for its activation as do the other pho regulon promoters. These results suggest that the two promoters function alternately in responding to phosphate or carbon starvation, thus providing the cell with a means to adapt to these physiological stresses.

Role of the sigma 70 subunit of RNA polymerase in transcriptional activation by activator protein PhoB in Escherichia coli.

“…They contain at least one unit of the pho box, and some pho genes such as pstS and ugpB have two and three pho boxes tandemly re1Corresponding author. peated, respectively (Kimura et al 1989;Kasahara et al 1991). Deletion analysis of these promoter regions also indicated that the pho box proximal to the -10 region is required for the expression of these genes.…”

PhoB transcriptional activator binds hierarchically to pho box promoters

“…The comparison of the PhoB E -DNA arrangement in the complex with a 23-bp DNA-mer (Blanco et al , 2002 ), which forms pseudo-continuous protein-DNA fibers, with the one in complex with a 26-bp DNA-mer (this work) reveals that the higher DNA bending in the former promotes contacts between adjacent PhoB E dimers. A previous in vivo study on transcription using pho box deletions of the ugpB promoter fused to a reporter gene also gave clues about hierarchical and cooperative binding (Kasahara et al , 1991 ). Although the authors did not relate their findings to cooperative binding, their results showed that at cellular concentrations of PhoB the intermediate pho box was required for the protein to bind to the downstream box and activate transcription.…”

Phosphate concentration regulates transcription of the Acinetobacter polyhydroxyalkanoic acid biosynthetic genes

“…Transcriptional activation from E. coli pho-regulated promoters has been shown to be dependent on the product of the phoB gene, PhoB (16,20). To determine whether the pho-activated promoters identified within the Acinetobacter PHA biosynthetic gene locus behaved similarly to these promoters, primer extensions were performed on RNA isolated from E. coli wild-type and phoB mutant strains containing pJKD1425.…”