Characterization of a cta/CDE operon-like genomic region encoding subunits I-III of the cytochrome c oxidase of the cyanobacterium Synechocystis PCC 6803.

Strong heterologous hybridization of a synthetic oligonucleotide probe of 17 bp originally used to clone subunit I of the Paracoccus denitrificans cytochrome c oxidase (M. Raitio, T. Jalli and M. Saraste (1987) EMBO J. 6, 2825-2833) to a single band was observed on Southern blots of Anacystis nidulans R2 (Synechococcus PCC 7942), Synechocystis PCC 6803, and Nostoc Mac PCC 8002 chromosomal DNA digests. Six pooled gene banks prepared from Synechocystis PCC 6803 contained regions that hybridized to the oligonucleotide (probe C) which is specifically directed toward the putative Cu-binding site VWAHHMY of subunit I. Two of these gene banks were transformed into Escherichia coli and screened for colonies hybridizing to probe C. Several clones were recovered, and one type of plasmid was identified from each gene bank. The two (overlapping) plasmids were called pDAUV1 and pDAUV2. A restriction map of the plasmids showed that the overlapping region contained an 80 bp PvuI-KpnI fragment binding to probe C. The two clones together permitted sequencing of the entire gene for cytochrome c oxidase subunit I from Synechocystis PCC 6803. Further systematic sequencing of approximately 1000 bp upstream and downstream each of the ctaD (subunit I) gene revealed the presence of two genes encoding subunits II (ctaC gene) and III (ctaE gene) due to conspicuous similarities to homologous genes from other cytochrome c oxidase-containing organisms. Yet, no indications of genes encoding additional subunits of the oxidase were found within the region sequenced.