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Blocking Chromosome Translocation during Sporulation of Bacillus subtilis Can Result in Prespore-Specific Activation of ^G That Is Independent of ^E and of Engulfment

Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140

Received 24 May 2006/ Accepted 1 August 2006

Formation of spores by Bacillus subtilis is characterized by cell compartment-specific gene expression directed by four RNA polymerase factors, which are activated in the order ^F-^E-^G-^K. Of these, ^G becomes active in the prespore upon completion of engulfment of the prespore by the mother cell. Transcription of the gene encoding ^G, spoIIIG, is directed in the prespore by RNA polymerase containing ^F but also requires the activity of ^E in the mother cell. When first formed, ^G is not active. Its activation requires expression of additional ^E-directed genes, including the genes required for completion of engulfment. Here we report conditions in which ^G becomes active in the prespore in the absence of ^E activity and of completion of engulfment. The conditions are (i) having an spoIIIE mutation, so that only the origin-proximal 30% of the chromosome is translocated into the prespore, and (ii) placing spoIIIG in an origin-proximal location on the chromosome. The main function of the ^E-directed regulation appears to be to coordinate ^G activation with the completion of engulfment, not to control the level of ^G activity. It seems plausible that the role of ^E in ^G activation is to reverse some inhibitory signal (or signals) in the engulfed prespore, a signal that is not present in the spoIIIE mutant background. It is not clear what the direct activator of ^G in the prespore is. Competition for core RNA polymerase between ^F and ^G is unlikely to be of major importance.

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