NUCLEOTIDE-SEQUENCE OF THE HEME SUBUNIT OF FLAVOCYTOCHROME C FROM THEPURPLE PHOTOTROPHIC BACTERIUM, CHROMATIUM-VINOSUM - A 2.6-KILOBASE PAIR DNA FRAGMENT CONTAINS 2 MULTIHEME CYTOCHROMES, A FLAVOPROTEIN, AND A HOMOLOG OF HUMAN ANKYRIN

The gene for the cytochrome subunit of Chromatium vinosum flavocytochr ome c (sulfide dehydrogenase) was cloned from an EcoRI digest of chrom osomal DNA. The mature cytochrome subunit contains 175 amino acid resi dues and two heme binding sites in agreement with the previously repor ted amino acid sequence. There is also a signal peptide of 25 residues , which apparently directs the protein to the periplasmic space. There are two open reading frames upstream of the heme subunit gene, which encode a tetraheme cytochrome c and a homolog of human ankyrin. The ge ne for the flavoprotein subunit of flavocytochrome c is in frame 15 nu cleotides downstream of the stop codon for the cytochrome gene. Messen ger RNA was isolated from malate grown cells. The transcript is approx imately 3 kilobases in size and does not hybridize with a probe contai ning the tetraheme cytochrome gene and part of the ankyrin homolog gen e. The heme subunit and flavoprotein subunit genes thus appear to form an operon. The flavoprotein subunit has a 30-residue signal peptide. The clone ends 95 amino acids into the N-terminal sequence of the matu re flavoprotein subunit (which should contain about 400 residues). The apparently periplasmic location of flavocytochrome c has important co nsequences for the presumed function as a sulfide dehydrogenase, becau se sulfur, which is the product of oxidation, is stored in the cytopla sm. Our results on the location of the enzyme are incompatible with th is function.