STRUCTURAL, TRANSCRIPTIONAL, AND PHYLOGENETIC ANALYSES OF THE ATPB GENE-CLUSTER FROM THE PLASTID OF CRYPTOMONAS-PHI (CRYPTOPHYCEAE)

Genes encoding the beta and epsilon subunits of the H+-adenosine triphosphatase complex have been identified in the large single-copy region of the plastid genome from the marine chlorophyll c-containing alga Cryptomonas PHI. Sequence analysis shows that the two genes do not overlap as in most land plants but, rather, are separated by a short 11-bp intergenic region, The genes lack introns and encode poly-peptides of 475 and 131 amino acids, respectively. The two genes are co-transcribed, producing a transcript of approximately 2000 nucleotides. Primer extension analysis of the 5' end of the transcript indicates two termini, one more prominent than the other. Sequence motifs typical of chloroplast promoters are located at -10 and -35 bp from both of these termini. Upstream of the atpBE operon is a gene with similarity to ORF167 of land plant plastids, and downstream is ORF281, which is homologous to a similarly located open reading frame from a brown alga. Phylogenetic analysis of atpB sequences from a variety of eubacteria and plastids shows all plastids arising from a single origin within the cyanobacteria and a clear dichotomy between the green and non-green lineages, in agreement with trees based on plastid small-subunit ribosomal RNA sequences.