Tethering of the Bacillus subtilis σ^E proprotein to the cell membrane is necessary for its processing but insufficient for its stabilization

σ^E, a sporulation-specific transcription factor of Bacillus subtilis, is synthesized as an inactive proprotein with a 27-amino acid extension at its amino terminus. This "pro" sequence is removed by a developmentally regulated protease, but when present, it blocks σ^E activity, tethers σ^E to the bacterium's cytoplasmic membrane, and promotes σ^E stability. To investigate whether pro-σ^E processing and/or stabilization are tied to membrane sequestration, we used fluorescent protein fusions to examine the membrane binding of SigE variants. The results are consistent with membrane association as a prerequisite for pro-σ^E processing but not as a sufficient cause for the proprotein's stability.