Multiple regulators and their interactions in vivo and its in vitro with the cbb regulons of Rhodobacter capsulatus

The cbb(I) and cbb(II) operons encode structural genes which are important for carbon dioxide fixation via the Calvin-Benson-Bassham reductive pentose phosphate pathway in Rhodobacter capsulatus. Each operon is regulated by c ognate LysR-type transcriptional activators, CbbR(I) and CbbR(II), with the product of the cbbR(I) gene, CbbR(II), able to control its own transcripti on under some growth conditions. Furthermore, CbbR(I) may at least partiall y regulate the cbb(II) operon, with significant, yet regulated transcriptio n of the cbb(II) operon occurring in the absence of any CbbR. These results suggested the importance of additional regulators. Thus, in addition to th e rather specific control exerted by CbbR, a more globally significant regu latory system, the RegA-RegB (PrrA-PrrB) two-component system, was found to contribute to transcriptional regulation of each cbb operon. The regA and regB mutant strains were found to contain constitutive levels of form I and form II RubisCO, the major proteins encoded by the cbb(I) and cbb(II), ope rons, respectively. In addition, DNaseI footprint analyses indicated that R egA*, a constitutively active mutant form of RegA, binds specifically to cb b(I) and cbb(II) promoter-operator regions. CbbR(I), CbbR(II), and RegA bin ding loci were localized relative to transcription start sites, leading to a coherent picture of how each of these regulators interacts with specific promoter-operator sequences of the cbb operons. (C) 2000 Academic Press.