A cytochrome bc1-complex of Rs. rubrum was isolated and the three subunits were purified to homogeneity. The N-terminal amino acid sequence of the purified subunits was determined by automatic Edman degradation. The pet genes of Rhodospirillum rubrum coding for the three subunits of the cytochrome bc1-complex were isolated from a genomic library of Rs. rubrum using oligonucleotides specific for conserved regions of the subunits from other organisms and a heterologous probe derived from the genes for the complex of Rb. capsulatus. The complete nucleotide sequence of a 5500 bp SalI/SphI fragment is described which includes the pet genes and three additional unidentified open reading frames. The N-terminal amino acid sequence of the isolated subunits was used for the identification of the three genes. The genes encoding the subunits are organized as follows: Rieske protein, cytochrome b, cytochrome c1. Comparison of the N-terminal protein sequences with the protein sequences deduced from the nucleotide sequence showed that only cytochrome c1 is processed during transport and assembly of the three subunits of the complex. Only the N-terminal methionine of the Rieske protein is cleaved off. The similarity of the deduced amino acid sequence of the three subunits to the corresponding subunits of other organisms is described and implications for structural features of the subunits are discussed.

A third group of antibiotics, the aurachins, have been isolated from the myxobacterium Stigmatella aurantiaca. The aurachins chemically are quinolones. and four of them (aurachins A-D) have been tested for their inhibitory activity in photosystem II and cytochrome b/c-complexes. Aurachin C is the best inhibitor in photosystem II (pI50-value 7.2); its biochemical behaviour being the same like that of other photosystem II herbicides. Both aurachins C and D are also excellent inhibitors in the cytochrome b6/f-complex (pI50-values of 7.00 and 7.49. respectively). In its mechanism of action, aurachin C resembl|es antimycin, whereas aurachin D is different from either antimycin or myxothiazol.

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