Bacillus subtilis DesR functions as a phosphorylation-activated switch to control membrane lipid fluidity

The Des pathway of Bacillus subtilis regulates the synthesis of the cold-shock induced membrane-bound enzyme Δ5-fatty acid desaturase (Δ5-Des). A central component of the Des pathway is the response regulator, DesR, which is activated by a membrane-associated kinase, DesK, in response to a decrease in membrane lipid fluidity. Despite genetic and biochemical studies, specific details of the interaction between DesR and the DNA remain unknown. In this study we show that only the phosphorylated form of protein DesR is able to bind to a regulatory region immediately upstream of the promoter of the Δ5-Des gene (Pdes). Phosphorylation of the regulatory domain of dimeric DesR promotes, in a cooperative fashion, the hierarchical occupation of two adjacent, non-identical, DesR-P DNA binding sites, so that there is a shift in the equilibrium toward the tetrameric active form of the response regulator. Subsequently, this phosphorylation signal propagation leads to the activation of the des gene through recruitment of RNA polymerase to Pdes. This is the first dissected example of a transcription factor functioning as a phosphorylation-activated switch for a cold-shock gene, allowing the cell to optimize the fluidity of membrane phospholipids.This work was supported in part by a grant from the Agencia Nacional de Promoción Científica y Tecnológica (FONCyT) (to D. de M.) and Special Action BMC2002-11562-E and SAF2001-05040-E from the Ministerio de Educación Ciencia (to M. E.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.Peer Reviewe