FIGURE 5: Cascade of sporulation-specific σ factors in B. subtilis. Immediately after polar septation, σ^F is activated in the forespore. σ^F activation triggers an intercompartmental signaling cascade that leads to the activation of σ^E in the mother cell. Together σ^F and σ^E control gene expression during engulfment. Roughly coincident with the completion of engulfment, σ^F is replaced by σ^G in the forespore, which leads to the subsequent activation of σ^K in the mother cell. σ^G and σ^K control gene expression in the forespore and the mother cell, respectively, after engulfment.