A diagrams how the pseudo-PP2C phosphatase RssB destabilizes σS by acting as an adapter protein for ClpXP proteolysis. B is a ribbon diagram of RssB (PDB ID 3F7A). The PP2C phosphatase domain is grey, the switch helices are orange, and the regulatory region is blue. The positions of bypass suppressor amino acid substitutions (residues 149, 156, 160, 164, 220, 222, 224, 227, 228, 260, 261, and 263 from P. aeruginosa corresponding to residues 146, 150, 154, 158, 214, 216, 218, 221, 222, 254, 255, and 257 from E. coli) that render RssB active in the absence of stress are indicated with spheres. C shows a comparison of the RssB dimer (above) and the SpoIIE457-827 dimer (below). The structures are colored as in panel A.