Abstract
The complete nucleotide sequence of the gene encoding the cytochrome subunit of the photosynthetic reaction centre from the purple bacterium Rhodopseudomonas viridis, and the derived amino acid sequence are presented. The nucleotide sequence of the gene reveals the existence of a typical bacterial signal peptide of 20 amino acid residues which is not found in the mature cytochrome subunit. The gene encoding the cytochrome subunit is preceded by the gene encoding the M subunit. Both genes overlap by 1 bp. The mature cytochrome subunit consists of 336 amino acid residues; 73% of its amino acid sequence was confirmed by protein sequencing work. The mol. wt of the cytochrome subunit including the covalently bound fatty acids and the bound heme groups is 40 500. The internal sequence homology is low, despite the symmetric structure of the cytochrome subunit previously shown by X-ray crystallographic analysis of the intact photosynthetic reaction centre. Sequence homologies to other cytochromes were not found.