The complete nucleotide sequence of the cytochrome c-554 gene from the green photosynthetic bacterium Chloroβexus aurantiacus has been determined. The derived amino acid sequence showed that the cytochrome precursor protein consists of 414 residues and contains 4-Cys-X-X-Cys-Hisheme binding motifs. The only regions of the cytochrome c-554 sequence that were found to be significantly similar to the sequences of cytochromes from other organisms were the heme binding sites. The highest similarity was found with the heme binding segments in the four-heme reaction center cytochrome subunit from the purple photosynthetic bacterium Rhodopseudomonas viridis. The importance of this similarity for the evolutionary relationship between Chloroβexus and the purple bacteria is discussed.
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