Disappearance of the s Transcription Factor from the Forespore and the SpoIIE Phosphatase from the Mother Cell Contributes to Establishment of Cell-Specific Gene Expression during Sporulation in Bacillus subtilis

We used immunofluorescence microscopy to investigate mechanisms governing the establishment of cellspecific gene transcription during sporulation in the bacterium Bacillus subtilis. The transcription factors s and s are synthesized shortly after the start of sporulation but do not become active in directing gene transcription until after polar division, when the activity of s is confined to the mother cell and the activity of s is restricted to the forespore. We show that shortly after septation, s and its proprotein precursor pro-s appear to be absent from the forespore and that a null mutation in spoIIIE, a gene known to be required for the translocation of a chromosome into the forespore, allows s and/or pro-s to persist and s to become active in the forespore. These findings suggest that the loss of s/pro-s from the forespore contributes to the compartmentalization of s-directed gene transcription. We also investigated the distribution of SpoIIE, a regulatory phosphatase required for the activation of s which exhibits a bipolar pattern of localization shortly after the start of sporulation. Normally, SpoIIE rapidly disappears from the sporangium, first from the mother-cell pole and then from the forespore pole. Here we show that a null mutation in spoIIIE causes the SpoIIE phosphatase to persist at both poles. The persistence of the SpoIIE phosphatase at the mother-cell pole could explain the lack of compartmentalization of s activity observed in a spoIIIE null mutant. We conclude that the establishment of cell-specific gene transcription involves the loss of s/pro-s from the forespore and the loss of the SpoIIE phosphatase from the mother-cell pole and that both processes are dependent upon the SpoIIIE protein.