Nucleotide Sequence of the Gene Coding for Four Subunits of Cytochrome c Oxidase from the Thermophilic Bacterium PS3

Abstract

The gene coding for four subunits of cytochrome aa₃-type oxidase was isolated from a genomic DNA library of the thermophilic bacterium PS3 and sequenced. The N-terminus of each subunit was also sequenced to verify the initiation site of the reading frame. The deduced amino acid sequences contained 615 amino acid residues for subunit I (CO1/ caaB product), 333 residues for subunit II (CO2/ caaA product), 207 residues for subunit III (CO3/ caaC product), and 109 residues for subunit IV (CO4/ caaD product) after processing. Re-examination of the sequencing of caa revealed a longer open reading frame for C01, which contains 14 transmembrane segments instead of 12 [ Sone et al. (1988) J. Biochem. 103, 606-610], although the main portions of the sequences constituting cytochrome a (Fe_A), cytochrome a₃ (Fe_B), and Cu_B are correct. PS3 CO2 has an additional sequence for cytochrome c after the Cu_A binding protein portion with 2 transmembrane segments, which is homologous to the mitochondrial counterpart. PS3 CO3 has DCCD-binding glutamyl residues but contains only 5 transmembrane segments, unlike the mitochondria' counterpart, which has 7 segments. The subunits of PS3 cytochrome oxidase (aa3-type) show clear similarity in amino acid sequences with those of cytochrome bo-type oxidase from Escherichia coli as well, in spite of the difference of hemes. PS3 CO3 and C04 are much more similar to E. coli CO3 and C04 than to mitochondrial CO3 and C04, respectively.