Modeling of early sporulation in Bacillus subtilis with hybrid functional Petri net

Spore formulation in Bacillus subtilis is induced under unfavorable growth conditions such as nutrient deprivation and high cell densities. In early stage of sporulation, the cell divides asymmetrically into two compartments, a smaller prespore and a larger mother cell. These remain attached but initiate different programs of transcription by cell-type-specific transcription factors (σ factors) [1]. For example, the σ is active only in the prespore while the σ is active only in the mother cell. Especially, the role of σ is vital because its correction activation essential for regulating other sigma factors of sporulation. Its regulation depends on three other proteins, SpoIIAB (AB), SpoIIAA (AA) and SpoII (E). AB is dual-functional: it can form a complex with, and thus inactivate, σ, and it can act as a specific protein kinase that phosphorylate AA to AA-P. AA-P is hydrolyzed to AA by E, a serine phosphatase. AA interacts with the σ-AB-ATP complex, releasing σ, which binds the core RNA polymerase to form the active σ holoenzyme (Fig.1).