IDENTIFICATION OF THE CONTIGUOUS PARACOCCUS-DENITRIFICANS CCMF AND CCMH GENES - DISRUPTION OF CCMF, ENCODING A PUTATIVE TRANSPORTER, RESULTS IN FORMATION OF AN UNSTABLE APOCYTOCHROME-C AND DEFICIENCY IN SIDEROPHORE PRODUCTION

Apocytochrome c(550) was detected in the periplasm of a new mutant of Paracoccus denitrificans, HN48, that is pleiotropically lacking c-type cytochromes, produces reduced levels of siderophores and carries a Tn 5 insertion in the ccmF gene for which sequence data, along with that for the contiguous ccmH, are reported. A counterpart to the ccmF gene was found in an archaebacterium but could not be located in the yeast genome, whereas mitochondrial haem lyases in the latter were not prese nt in an archaeobacterial or in eubacterial genomes. A topological ana lysis for CcmF is presented which indicates at least eleven transmembr ane helices, suggesting a role as a transporter; evidence against the substrate being haem is presented but sequence similarity with Escheri chia coli gamma-aminobutyric acid transporter was identified. Analysis by pulse-chase methodology has shown that, in this and another cytoch rome-c-deficient mutant, the apo form of P. denitrificans cytochrome c (550) is much less stable than the hole form, directly demonstrating t he presence of a periplasmic degradation system in P. denitrificans th at removes non-functional proteins. A variety of phenotypes are observ ed for P. denitrificans mutated in different ccm genes, thus indicatin g that the stability of the ccm gene products does not require assembl y of a complex of all the Ccm proteins.