Nucleotide sequence of cDNA clones encoding the entire precursor polypeptides for subunits IV and V of the photosystem I reaction center from spinach

Abstract

Using lgtl 1 expression cloning and immunoscreening, CDNA-containing recombinant phages for subunits IV and V of the photosystem I reaction center were isolated, sequenced and used to probe Northern blots of polyadenylated RNA prepared from spinach seedlings. The mRNA sizes for both components are _ 1000 and 850 nucleotides, respectively. The 968 nucleotide cDNA sequence and derived amino acid sequence for subunit IV predict a single open reading frame of 231 amino acid residues (25.4 kDa). Comparison with a 13-residue N-terminal amino acid sequence determined for subunit IV suggests a mature protein of 17.3 kDa (154 residues) and a transit sequence of 77 amino acids (8.1 kDa). The corresponding data for subunit V are 677 bp (cDNA), 167 residues for the precursor protein (18.2 kDa), 98 residues for the mature polypeptide (10.8 kDa) and 69 residues for the transit peptide (7.4 kDa). Secondary structure predictions indicate that both proteins possess greatly different transit sequences and that none is membrane-spanning.

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

“…The sequence of the 12 kDa protein ( fig.2C) shows homology with that of 17 kDa protein of Synechococcus PCC 7002, and very limited homology with spinach subunit V, designated psaG [16]. However, appreciable homology can be seen in internal sequence between the 17 kDa protein of Synechococcus PCC 7002 and the subunit V of spinach and pea, although the corresponding region for the S. vulcanus protein was not determined in this study.…”

“…The sequence of the 14 kDa protein ( fig.2B) shows homology with that of spinach subunit IV, whose gene has been designated psaF [16].…”

“…Interestingly, the homology between the 14 kDa and subunit IV is high in N-terminal part while low in the internal part. In spinach, the subunit IV is suggested to be attached on the lumen side of the PSI complex, since its mature protein sequence is preceded by a presequence having an amphipathic fl-sheet and a hydrophobic domain in its Cterminal part, both of which are peculiar to lumenlocated proteins such as plastocyanin and PS II extrinsic proteins related to water oxidation [16]. If so, the cyanobacterial homologue might also be processed when translocated into the lumen space of thylakoids.…”

“…In cyanobacteria, however, neither a protein nor a gene corresponding to the iron-sulfur center-carrying component has been identified yet, although there are many functional and molecular biological indications of its presence [12][13][14]. The other core components of higher plants so far sequenced are all encoded by nuclear genome and their sequences vary considerably among plant species [15][16][17][18][19][20]. Some such core components from cyanobacteria have been also sequenced, but only one component has been proven to correspond to a higher plant homologue (subunit II or psaD product) [4,21,22].…”

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.…”