BACILLUS-SUBTILIS PRO-SIGMA(E) FUSION PROTEIN LOCALIZES TO THE FORESPORE SEPTUM AND FAILS TO BE PROCESSED WHEN SYNTHESIZED IN THE FORESPORE

Endospore formation in Bacillus subtilis begins with an asymmetric cel l division that partitions the bacterium into mother cell and forespor e compartments, Mother cell-specific gene expression is initiated by s igma(E), a transcription factor that is active only in the mother cell but which existed as an inactive precursor (pro-sigma(E)) in the pred ivisional cell, Activation of pro-sigma(E) involves the removal of 27 amino acids from its amino terminus, A chimera of pro-sigma(E) and the green fluorescent protein (GFP) was expressed from either the normal sigE promoter (P-spoIIG), which places pro-sigma(E)::GFP in both mothe r cell and forespore compartments, or the forespore-specific promoter (P-spoIIG), which produces pro-sigma(E)::GFP only in the forespore com partment. The pro-sigma(E)::GFP expressed from P-spoIIG, but not P-dac F, was converted to a lower-molecular-weight form by a mechanism depen dent on gene products (SpoIIGA and sigma(F)) that are essential for no rmal pro-sigma(E) processing, This finding is consistent with the pro- sigma(E) processing reaction occurring only in the mother cell compart ment, In processing-deficient cells, pro-sigma(E)::GFP was found to ac cumulate at the septal membrane, a location where its processing appar atus would be susceptible to triggering from the adjoining forespore.