A sixth subunit of ATP synthase, an F(0) component, is encoded in the pea chloroplast genome.

DNA from pea and tobacco chloroplasts hybridizes specifically with probes derived from the gene for a membrane component, the a subunit of ATP synthase of the cyanobacterium, Synechococcus 6301. DNA sequence of the hybridizing region of the pea plastid DNA has revealed that it encodes a protein of 247 amino acids related in sequence to the a subunits of ATP synthase of Escherichia coli, Synechococcus and mitochondria. This is the sixth component of chloroplast ATP synthase that is plastid coded. The gene is located upstream from the genes for three other ATP synthase subunits and a transcript of 6 kb contains coding sequences from each of these genes. Thus the subunit a gene is part of a co-transcribed cluster of four ATP synthase genes arranged in the order a:c(or III):b(or I):alpha. Two other ATP synthase genes, those for beta and epsilon subunits, are known to form a separate cluster. These gene arrangements are most closely related to those found in the cyanobacterium, Synechococcus 6301. Hence, this finding provides strong evidence for a common origin for cyanobacteria and plant chloroplasts.