Organization and sequences of genes for the subunits of ATP synthase in the thermophilic cyanobacterium Synechococcus 6716

Abstract

The sequences of the genes for the nine subunits of ATP synthase in the thermophilic cyanobacterium Synechococcus 6716 have been determined. The genes were identified by comparison of the encoded proteins with sequences of ATP synthase subunits in other species, and confirmed for subunits alpha, beta, delta and epsilon, by determining their N-terminal sequences. They are arranged at three separate loci. Six of them are in one cluster in the order a: c: b': b: delta: alpha, and those for the beta and epsilon subunits form a second and separate cluster. The gene for the gamma-subunit is at a third site. As in other bacteria, the gene for subunit a is immediately preceded by a gene coding for a small hydrophobic protein of unknown function, known as uncI in Escherichia coli. The gene orders in Synechococcus 6716 are related to the orders of ATP synthase genes in the plastid genomes of higher plants, and particularly of a red alga and a diatom. The sequences of the subunits are similar to those of chloroplast ATP synthase, the alpha, beta and c subunits being particularly well conserved. Differences in the primary structures of the Synechococcus 6716 and chloroplast gamma subunits probably underlie different mechanisms of activation of ATP synthase. The nucleotide sequences that are presented also contain 12 other open reading frames. One of them encodes a protein sequence related to the E. coli DNA repair enzyme, photolyase, and another codes for a protein that contains internal repeats related to sequences in the myosin heavy chain.