Signal transduction in the control of phosphate-regulated genes of Escherichia coli

Abstract

Bacteria such as Escherichia coli regulate the synthesis of a large number of proteins in response to extracellular inorganic phosphate (P i ) levels by activating transcription of co-regulated genes. More than 80 proteins are synthesized in increased amounts in response to P i limitation in the gram-negative bacterium E. coli [1-3]. Many of these proteins are the products of a set of co-regulated genes known as the phosphate (Pho) regulon. Altogether 38 Pho regulon genes have now been characterized (by cloning, sequencing, mutational analysis, and/or examination of their gene products) in E. coli, or the closely related bacteria Enterobacter aerogenes and Salmonella typhimurium [4]. These genes are arranged in eight (or more) transcriptional units, and their gene products probably all have a role in the assimilation of alternative phosphorus (P) sources from the environment. Their transcription requires an upstream activation site (called a Pho Box) and a DNA-binding protein (called PhoB) that acts as a transcriptional activator only when it is phosphorylated (Fig. 1). The level of expression of Pho regulon genes is regulated by the amount of phospho-PhoB.