PsbA in the marine chromophyte Heterosigma carterae: evolutionary analysis and comparative structure of the D1 carboxyl terminus

Abstract

The 32 kDa D1 protein, encoded by the psbA gene, is a component of photosystem II in photosynthetic eukaryotes and cyanobacteria. In the chi a,c‐containing alga Heterosigma carterae (previously referred to as Olisthodiscus luteus), psbA is transcribed as a 1.7‐kb monocistronic message. The transcription start site and putative prokaryotic‐like –10 (TATAAT) and –35 (GTGATT) promoter domains have been identified for this gene, which encodes a protein that is 360 amino acids in length. The protein contains a seven amino acid motif near the carboxyl terminus that is also present in non‐chl b‐containing algal plastids and cyanobacteria, but not in terrestrial plants, green algae, or the prokaryote Prochlorothrix. Phylogenetic analysis of D1 sequences, with special attention to the seven amino acid motif, suggests that plastids of rhodophytic and chromophytic algae form an evolutionary lineage distinct from cyanobacteria and chlorophytic (chi a,b‐ containing) chloroplasts. A model for the function of the seven amino acid motif is proposed.