The tyrosine kinase McsB is a regulated adaptor protein for ClpCP.

Cells of the soil bacterium Bacillus subtilis have to adapt to fast environmental changes in their natural habitat. Here, we characterized a novel system in which cells respond to heat shock by regulatory proteolysis of a transcriptional repressor CtsR. In B. subtilis, CtsR controls the synthesis of itself, the tyrosine kinase McsB, its activator McsA and the Hsp100/Clp proteins ClpC, ClpE and their cognate peptidase ClpP. The AAA+ protein family members ClpC and ClpE can form an ATP-dependent protease complex with ClpP and are part of the B. subtilis protein quality control system. The regulatory response is mediated by a proteolytic switch, which is formed by these proteins under heat-shock conditions, where the tyrosine kinase McsB acts as a regulated adaptor protein, which in its phosphorylated form activates the Hsp100/Clp protein ClpC and targets the repressor CtsR for degradation by the general protease ClpCP.