Figure 5.

Model of heme-responsive control of components of the respiratory chain by HrrSA. The results of this study reveal HrrSA as a global regulator of heme homeostasis coordinating the expression of genes involved in heme biosynthesis, oxidative stress responses, glucose uptake and cell envelope remodeling. Genes encoding the components of the branched respiratory chain of Corynebacterium glutamicum comprise an important part of the HrrA regulon. While HrrA acts as an activator of almost all components (ctaE-qcrCAB, ctaB, cydAB), it represses transcription of the sigC gene encoding an important sigma factor required for cydAB expression. This regulatory network architecture consequently confers prioritization to the synthesis of the more efficient proton pump, the cytochrome bc₁–aa₃ supercomplex. Bordered boxes, b, c, a, d: heme b, heme c, heme a, heme d.