The “Pro” Sequence of the Sporulation-Specific ς Transcription Factor ς(E) Directs It to the Mother Cell Side of the Sporulation Septum

ς(E), a mother cell-specific transcription factor of sporulating Bacillus subtilis, is derived from an inactive precursor protein (pro-ς(E)). Activation of ς(E) occurs when a sporulation-specific protease (SpoIIGA) cleaves 27 amino acids from the pro-ς(E) amino terminus. This reaction is believed to take place at the mother cell-forespore septum. Using a chimera of pro-ς(E) and green fluorescent protein (GFP) to visualize the intracellular location of pro-ς(E) by fluorescence microscopy, and lysozyme treatment to separate the mother cell and forespore compartments, we determined that the pro-ς(E)::GFP signal, localized to the forespore septum prior to lysozyme treatment, is restricted to the mother cell compartment after treatment. Thus, pro-ς(E)::GFP had been sequestered to the mother cell side of the septum. This segregation of pro-ς(E)::GFP, and presumably pro-ς(E), to the mother cell is likely to be the reason why ς(E) activity is restricted to that compartment.