"Various conditions in the environment are monitored by a group of five sensor kinases. These function via a phosphotransfer relay system whose mechanism resembles that of a two-component regulatory system ... but is considerably more complex (Figure 7.25). The net result of multiple adverse conditions is the successive phosphorylation of several proteins called sporulation factors, culminating with sporulation factor Spo0A. When Spo0A is highly phosphorylated, sporulation proceeds." \cite{brock2014}
Many of the signals, both positive and negative, that affect this decision are interpreted through the phosphorelay signal transduction system (
Burbulys et al. 1991).