INVOLVEMENT OF THE SENSOR KINASE ENVZ IN THE IN-VIVO ACTIVATION OF THE RESPONSE-REGULATOR PHOB BY ACETYL PHOSPHATE

Three signalling pathways lead to activation of the phosphate (Pho) re gulon by phosphorylation of the response-regulator PhoB in Escherichia coil. One pathway responds to the extracellular inorganic phosphate ( Pi) level and leads to activation by the Pi sensor kinase, PhoR. The o ther two pathways are Pi independent and are apparent in the absence o f PhoR. One Pi-independent pathway responds to the level of an unknown catabolite and leads to activation by the catabolite regulatory senso r kinase, CreC (originally called PhoM); the other Pi-independent path way responds to acetyl phosphate and leads to activation by a process requiring acetyl phosphate. Here we show that activation of PhoB by ac etyl phosphate can require the sensor kinase EnvZ. Accordingly, we pro pose that the in vivo activation of PhoB by acetyl phosphate (and perh aps other two-component response-regulators as well) probably always r equires a certain kinase that can vary depending upon the growth condi tions.