Identification of Novel Spx Regulatory Pathways in Bacillus subtilis Uncovers a Close Relationship between the CtsR and Spx Regulons.

In , the Spx transcription factor controls a large regulon in response to disulfide, heat, and cell wall stresses. The regulatory mechanisms that activate the Spx regulon are remarkably complex and involve changes in transcription, proteolysis, and posttranslational modifications. To identify genes involved in Spx regulation, we performed a transposon screen for mutations affecting expression of , an Spx-dependent gene. Inactivation of , encoding the regulator of the Clp proteases, reduced expression and lowered Spx levels. This effect required ClpP, but involved ClpC rather than the ClpX unfoldase. Moreover, cells lacking McsB, a dual function arginine kinase and ClpCP adaptor, largely reverted the phenotype and increased expression. The role of McsB appears to involve its kinase activity, since loss of the YwlE phosphoarginine phosphatase also led to reduced expression. Finally, we show that Spx is itself a regulator of the operon. Altogether, this work provides evidence for a role of CtsR regulon members ClpC, ClpP, and McsB in Spx regulation and identifies a new feedback pathway associated with Spx activity in In , the Spx transcription factor is proteolytically unstable, and protein stabilization figures prominently in the induction of the Spx regulon in response to oxidative and cell envelope stresses. ClpXP is largely, but not entirely, responsible for Spx instability. Here, we identify ClpCP as the protease that degrades Spx under conditions that antagonize the ClpXP pathway. Spx itself contributes to activation of the operon, which encodes ClpC as well as the McsB arginine kinase and protease adaptor, thereby providing a negative feedback mechanism. Genetic studies reveal that dysregulation of the CtsR regulon or inactivation of the YwlE phosphoarginine phosphatase decreases Spx activity through mechanisms involving both protein degradation and posttranslational modification.