THE PET OPERON, ENCODING THE PROSTHETIC GROUP-CONTAINING SUBUNITS OF THE CYTOCHROME BC(1) COMPLEX, OF THE PURPLE SULFUR BACTERIUM CHROMATIUM-VINOSUM

The pet operon, encoding the prosthetic group-containing subunits of t he cytochrome bc(1) complex of the purple sulfur bacterium Chromatium vinosum, has been cloned and sequenced. The 5' to 3' order of the C. v inosum genes is: petA, encoding the Rieske iron-sulfur protein; petB, encoding cytochrome b; and petC, encoding cytochrome c(1). Cytochrome b is the best conserved subunit of the C. vinosum complex, when compar ed to the corresponding proteins from four photosynthetic purple non-s ulfur bacteria (70 to 74% identity). Identities for the C. vinosum Rie ske protein and those from purple non-sulfur bacteria range from 60 to 64%. The C-terminal region of the C. vinosum Rieske protein is quite similar to those of purple non-sulfur bacteria, while the N-terminal r egion is more closely related to mitochondrial Rieske proteins of orga nisms such as Neurospora crassa. Cytochrome c(1) is the least well-con served protein of the C. vinosum cytochrome bc(1) complex, with identi ties ranging from 49 to 51% when compared to the corresponding protein s from purple non-sulfur bacteria. A well-conserved negatively-charged region of the cytochromes c(1) of the purple non-sulfur bacteria, tho ught to be involved in binding the electron acceptor for the complex, cytochrome c(2), is absent in C. vinosum cytochrome c(1). A positive S outhern hybridization using a probe constructed from the Rhodobacter s phaeroides fbcQ gene, which codes for a fourth subunit of the cytochro me bc(1) complex in that bacterium, suggests the presence of a homolog ous gene in C. vinosum.