DIFFERENTIAL LEVELS OF SPECIFIC CYTOCHROME-C BIOGENESIS PROTEINS IN RESPONSE TO OXYGEN - ANALYSIS OF THE CCL OPERON IN RHODOBACTER-CAPSULATUS

The photosynthetic bacterium Rhodobacter capsulatus synthesizes c-type cytochromes under a variety of growth conditions, For example, under aerobic growth, c-type cytochromes are synthesized as part of an elect ron transport pathway, using oxygen as the terminal electron acceptor, Anaerobically in the light, R. capsulatus requires cytochrome bc(1) a nd other c-type cytochromes for the photosynthetic electron transport pathway, It is shown here that the ccl1 and ccl2 genes of R. capsulatu s are required for the synthesis of all c-type cytochromes, including the cytochrome c' protein of unknown function but of structural simila rity to cytochrome b(562). Polar and nonpolar mutations constructed in each gene demonstrated that the ccl12 genes form an operon, Expressio n of the ccl12 genes was examined by using lacZ and phoA fusions as tr anslational reporters, Primer extension analysis was used to determine transcriptional control and the start site of the ccl12 promoter, Fin ally, antiserum to the Ccl2 protein was used to quantitate levels of C cl2 under six different growth conditions, The Ccl2 protein is present at 20-fold-higher levels under conditions where oxygen is present, In contrast, other cytochromes c biogenesis proteins, HelA and HelX, pre viously shown to be part of an helABCDX operon, are at relatively simi lar levels under these six growth Conditions, This discovery is discus sed in terms of the physiology and evolution of cytochromes c biogenes is, with particular attention to oxidative environments.