Required for the biogenesis of c-type cytochromes. Interacts with FloT. Present in detergent-resistant membrane (DRM) fractions that may be equivalent to eukaryotic membrane rafts; these rafts include proteins involved in signaling, molecule trafficking and protein secretion. Cells lacking this gene exhibit a lack of cytochromes c but normal contents of cytochrome a and b. Can sporulate. Belongs to the CcmF/CycK/Ccl1/NrfE/CcsA family.