ESCHERICHIA-COLI CCM IN-FRAME DELETION MUTANTS CAN PRODUCE PERIPLASMIC CYTOCHROME-B BUT NOT CYTOCHROME-C

Escherichia coli CcmA, CcmB and CcmC polypeptides are required for cyt ochrome c synthesis and are thought to constitute the subunits of an A BC-type transporter as judged from sequence data, Using a periplasmic reporter system based on Bacillus subtilis cytochrome c-550 and E. col i cytochrome b-562 we show that the synthesis of the b-type cytochrome in the periplasm is normal in E, coli ccmA and ccmC in-frame deletion mutants, Mutants deleted for ccmF or ccmG encoding a component of a p utative cytochrome c-heme lyase and a membrane bound thioredoxin-like protein, respectively, have the same phenotype, The ccm mutants produc e cytochrome c-550 polypeptide, but not holocytochrome c, Taken togeth er the results demonstrate that heme can be transported to the peripla sm by a ccm-independent mechanism. (C) 1997 Federation of European Bio chemical Societies.