The pet operon, encoding the prosthetic group-containing subunits of the cytochrome bc1 complex, of the purple sulfur bacterium Chromatium vinosum

Abstract

The pet operon, encoding the prosthetic group-containing subunits of the cytochrome bc 1 complex of the purple sulfur bacterium Chromatium vinosum, has been cloned and sequenced. The 5′ to 3′ order of the C. vinosum genes is: petA, encoding the Rieske iron-sulfur protein; petB, encoding cytochrome b; and petC, encoding cytochrome c1. Cytochrome b is the best conserved subunit of the C. vinosum complex, when compared to the corresponding proteins from four photosynthetic purple non-sulfur bacteria (70 to 74% identity). Identities for the C. vinosum Rieske 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 region is more closely related to mitochondrial Rieske proteins of organisms such as Neurospora crassa. Cytochrome c1 is the least well-conserved protein of the C. vinosum cytochrome bc1 complex, with identities ranging from 49 to 51% when compared to the corresponding proteins from purple non-sulfur bacteria. A well-conserved negatively-charged region of the cytochromes c1 of the purple non-sulfur bacteria, thought to be involved in binding the electron acceptor for the complex, cytochrome c2, is absent in C. vinosum cytochrome c1. A positive Southern hybridization using a probe constructed from the Rhodobacter sphaeroides fbcQ gene, which codes for a fourth subunit of the cytochrome bc1 complex in that bacterium, suggests the presence of a homologous gene in C. vinosum.