FIG. 7.

Proposed model of cbb gene regulation in R. sphaeroides during chemoautotrophic growth. The Cbb3 cytochrome (Cyt) oxidase transmits an inhibitory signal to PrrB, resulting in a shift in the equilibrium towards unphosphorylated PrrA and subsequent lack of activation of the cbb_II promoter. Also shown is a signal derived from Cbb3 cytochrome oxidase activity going to an alternate transcriptional regulator that in turn activates the cbb_I promoter. The model depicts transcriptional activation of both cbb operons by CbbR in response to a signal that presumably reflects the carbon status of the cell.