A protease as a possible sensor of environmental conditions in E. coli outer membrane

A mutant strain devoid of the colicin A protease activity (cpr) located at the external face of the outer membrane has been isolated. The location of the mutation (about 74 min on the genetic map), its pleiotropic effects concerning mainly the protein composition of the outer membrane and sensitivity to phages and colicins, are very similar in cpr and in tpo, envZ, perA strains that are affected in the ompB locus. Conditions resulting in inhibition of the colicin A protease activity also result in transcriptional regulation of OmpF, OmpC, and LamB protein synthesis. The possibility for this protease as an osmosensor of the cell's external environment is discussed.