A forespore checkpoint for mother cell gene expression during development in B. subtilis.

Gene expression in the mother cell compartment of sporulating cells of B. subtilis is partly governed by the mother cell RNA polymerase sigma factor sigma K. Paradoxically, sigma K-directed gene expression also depends on sigma G, the product of the forespore compartment regulatory gene spoIIIG, and on other forespore regulatory proteins. We now identify mutations in the genes bofA and bofB that relieve the dependence of mother cell gene expression on forespore regulatory proteins but not on sigma K. We establish that the dependence of mother cell gene expression on the forespore regulatory proteins is mediated at the level of the conversion of pro-sigma K to its mature, active form. We propose that the bofA and/or bofB proteins govern this conversion in response to a signal generated by the forespore. Activation of pro-sigma K could be a checkpoint for coordinating gene expression between the mother cell and forespore compartments of the developing sporangium.