Expression of the Large ATP Synthase Gene Cluster from Spinach Chloroplasts

We have examined the expression of the spinach (Spinacia oleracea) chloroplast large ATP synthase gene cluster. This gene cluster encodes the small ribosomal subunit protein two (rps2), and four proteins of the ATP synthase protein complex: CF₀-IV (atpI), CF₀-III (atpH), CF₀-I (atpF), and CF₁-α (atpA). Experiments to specifically 5′ end label (cap) primary transcripts revealed two regions of transcription initiation, one located upstream of the rpen gene and the other upstream of atpH. Northern analysis revealed greater than thirty transcripts derived from this gene cluster, the majority of which are processing products derived from the primary transcripts. In addition, two RNA species were identified as containing the atpF intron in a lariat structure. Processing steps include splicing to remove the group II intron found in atpF, as well as endonucleolytic and exonucleolytic cleavages. An ordered series of processing steps is proposed.