A feeding tube model for activation of a cell-specific transcription factor during sporulation in Bacillus subtilis

Abstract

Spore formation by Bacillus subtilis takes place in a sporangium consisting of two chambers, the forespore and the mother cell, which are linked by pathways of intercellular communication. One pathway, which couples the activation of the forespore transcription factor σG to the action of σE in the mother cell, has remained mysterious. Traditional models hold that σE initiates a signal transduction pathway that specifically activates σG in the forespore. Recent experiments indicating that the mother cell and forespore are joined by a channel have led to the suggestion that a specific regulator of σG is transported from the mother cell into the forespore. As we report here, however, the requirement for the channel is not limited to σG. Rather, it is also required for the persistent activity of the early-acting forespore transcription factor σF as well as that of a heterologous RNA polymerase (that of phage T7). We infer that macromolecular synthesis in the forespore becomes dependent on the channel at intermediate stages of development. We propose that the channel is a gap junction-like feeding tube through which the mother cell nurtures the developing spore by providing small molecules needed for biosynthetic activity, including σG-directed gene activation.