Molecular cloning and nucleotide sequence of the psaA and psaB genes of the cyanobacterium Synechococcus sp. PCC 7002

Abstract

The psaA and psaB genes, which encode the P700 chlorophyll a apoproteins of the Photosystem I complex, have been cloned from the unicellular, transformable cyanobacterium Synechococcus sp. PCC 7002. The nucleotide sequence of these genes and of their flanking sequences have been determined by the chain termination method. As found in the chloroplast genomes of higher plants, the psaA gene lies 5' to the psaB gene; however, the cyanobacterial genes are separated by a greater distance (173 vs. 25-26 bp). The psaA gene is predicted to encode a polypeptide of 739 amino acid residues (81.7 kDa), and the psaB gene is predicted to encode a polypeptide of 733 residues (81.4 kDa). The cyanobacterial psa gene products are 76% to 81% identical to their higher plant homologues; moreover, because of conservative amino acid replacements, the cyanobacterial sequences are more than 95% homologous to those determined for higher plants. These results provide the basis for a genetic analysis of Photosystem I, and are discussed in relationship to structural and functional aspects of the Photosystem I complexes of both cyanobacteria and higher plants.

Identification of photosystem I components from the cyanobacterium, Synechococcus vulcanus by N‐terminal sequencing

“…Two proteins of 13 and 11 kDa in the peak PSI complex [8], whose N-terminal sequences do not correspond to any of other higher plants or S. vulcanus are reported. Since the homologues of subunits II, IV, and V and VII were detected in the pea complex, the 13 and 11 kDa proteins may correspond to the rest, subunit III or VI, although their partial Sequences show almost no homology.…”

“…Sequences of CP I apoproteins, encoded by chloroplast genes, psaA and psaB, are highly conserved not only among higher plants but also between higher plants and cyanobacteria [7,8]. The protein carrying the iron-sulfur centers A and B, which is encoded by a chloroplast gene, psaC, is also highly conserved among higher plants [9][10][11].…”

Photosystem I reaction‐centre proteins contain leucine zipper motifs

“…2. Comparison of the leucine repeat containing regions in the photosystem I reaction-centre polypeptides deduced from the psuA and psuB gene sequences from Synechococcus [17], Murchantiu [a], Chlamydomonas [18], tobacco [19], spinach [20], pea [213 and maize [22]. The conserved leucine repeats and iron-sulphur binding regions are in bold.…”

Polypeptide composition of higher plant photosystem I complex

“…'Native' PSI complex which additionally retains LHCI can be isolated from green plants by a milder detergent treatment, while cyanobacterial PSI has no LHCI-like antenna. Until recently the subunit proteins found in these various types of PSI complexes from both green plants and cyanobacteria have been classified in three categories as follows: (i) two chlorophyll a-binding subunits of about 80 kDa, which carry P700, acceptors A0 and A1, and Fe-S center X, (ii) 5-6 core subunits ranging from 8 to 22 kDa which include Fe-S center A/B protein, plastocyanin-docking protein and ferredoxin-docking protein, (iii) 4-5 LHCI subunits of Abbreviations: CPI, chlorophyll-protein complex 1 of photosystem I reaction center; LHCI, light-harvesting chlorophyll complex associated with photosystem I; PSI, photosystem I; SDS-PAGE, sodium dodecylsulfate-polyacrylamide gel electrophoresis green plants ranging from 15 to 25 kDa which bind antenna chlorophyll a and b. Sequencing of these proteins and/or their corresponding genes have registered two genes, psaA and psaB, for the P700-carrying proteins [2,3], 6 genes, psaC to psaH, for the core subunits [4][5][6][7][8][9][10][11][12][13][14][15][16][17] and at least three types of cab genes for the LHCI subunits [18][19][20]. In green plants, psaA, psaB and psaC are encoded by chloroplast genome while the others are encoded by nuclear genome.…”

“…In green plants, psaA, psaB and psaC are encoded by chloroplast genome while the others are encoded by nuclear genome. Sequence comparison indicates that the two P700-carrying proteins and most of the core subunits are more or less conserved between cyanobacteria and green plants [3,13,17], although LHCI is absent in cyanobacteria.…”