Cloning and Expression of Genes Encoding A 12 kDa Protein and Cytochrome c550, Two Extrinsic Proteins of PS II, from Ared Alga Cyanidium Caldarium

Abstract

Cytochrome c550 and the 12 kDa protein are two extrinsic proteins first found in PSII from prokaryotic cyanobacteria (1). They recently have been confirmed to be present in the PSII from a eukaryotic red alga, Cyanidium caldarium (2). These two components function in maintaining the maximum oxygen evolution in both cyanobacterial and red algal PSU, although their functions may not be exactly the same between the cyanobacteria and red algae (3–4). The genes for these two components are psbV and psbU, respectively; they have been cloned from several species of cyanobacteria (5–9). The psbV gene coding for cyt c550 has also been found in the plastid genomes of three species of eukaryotic algae, Cyanophora paradoxa (10), Porphyra purpurea (11) and Odontella sinensis (12) whose complete plastid genome sequences have been determined. Like in cyanobacteria, the psbV gene in these three eukaryotic algae bears a leader sequence encoding a transit peptide required for the transport of the cyt into the thylakoid lumen, consistent with a role of the cyt in PSII. On the contrary, in these plastid genomes, the psbU gene was not present, suggesting that this gene has been transferred to the nucleus during the evolution from prokaryotic cyanobacteria to eukaryotic algae.