The "Pro" sequence of the sporulation-specific sigma transcription factor sigma(E) directs it to the mother cell side of the sporulation septum

sigma(E), a mother cell-specific transcription factor of sporulating Bacill us subtilis, is derived from an inactive precursor protein (pro-sigma(E)). Activation of sigma(E) occurs when a sporulation-specific protease (SpoIIGA ) cleaves 27 amino acids from the pro-sigma(E) amino terminus. This reactio n is believed to take place at the mother cell-forespore septum. Using a ch imera of pro-sigma(E) and green fluorescent protein (GFP) to visualize the intracellular location of pro-sigma(E) by fluorescence microscopy, and lyso zyme treatment to separate the mother cell and forespore compartments, we d etermined that the pro-sigma(E)::GFP signal, localized to the forespore sep tum prior to lysozyme treatment, is restricted to the mother cell compartme nt after treatment. Thus, pro-sigma(E)::GFP had been sequestered to the mot her cell side of the septum. This segregation of pro-sigma(E)::GFP, and pre sumably pro-sigma(E), to the mother cell is likely to be the reason why sig ma(E) activity is restricted to that compartment.