Nucleotide sequence of the gene for apocytochrome <i>b</i>‐559 on the spinach plastid chromosome: implications for the structure of the membrane protein

Abstract

Analysis of a 0.6 kb fragment of the spinach plastic chromosome adjacent to the 3' end of the apocytochrome f gene has disclosed two uninterrupted reading frames of 83 and 39 triplets, the product of the first one being apocytochrome b ‐559. The first 27 predicted amino acid residues had been verified by protein sequence analysis and the molecular mass of 9390 Da derived from the amino acid sequence deduced here is close to that of the authentic protein. The two genes are transcribed by a bicistronic RNA in a direction opposite to that of cytochrome f , and their translation stop/potential ribosome binding sites overlap. Features of the two genes resembling those of bacterial genes include putative tetra‐ or pentanucleotide ShineDalgarno sequences, Pribnow boxes, ‘−35’ promotor consensus sequences and possibly a transcription termination region. Both gene structure and products of DNA‐ or RNA‐programmed cell‐free translation preclude that apocytochrome b ‐559 is made as a precursor. The amino acid sequence includes only one histidine residue located in a predicted secondary structure of strong hydrophobicity which indicates the intriguing possibility that more than one protein chain must cooperate in heme binding of this cytochrome.