Organization and co-transcription of four cbb gene clusters in A. ferrooxidans ATCC 23270. (A) cbb1 (B) cbb2 (C) cbb3 and (D) cbb4. The following are represented in each of the panels A-E: (a) nucleotide sequences of the predicted σ70-like promoter region (-10 and -35 sites in italics) and potential CbbR-binding sites in grey boxes with the LysR-type TNA-N7-TNA and T-N11-A consensus binding sites in bold letters, (b) gene organization of the respective operons with predicted rho-independent transcriptional stop sites indicated as stem-loop symbols, (c) locations of PCR primers used for RT-PCR experiments (indicated by numbers) or EMSA assays (indicated by letters) and (d) gel electrophoresis of fragments amplified by RT-PCR using purified cellular RNA as template. A 1-kb scale bar is shown. One of the T-N11-A consensus binding sites in the cbb4 operon is part of a larger pseudo-palindrome indicated by inverted arrows. Predicted gene functions are provided in Table 3.