title: Nucleotide sequences of cDNA clones encoding the entire precursor polypeptide for subunit VI and of the plastome-encoded gene for subunit VII of the photosystem I reaction center from spinach.
abstract: Recombinant phage which encode the entire precursor polypeptide for subunit VI of the photosystem I reaction center have been selected from a lambda gt11 cDNA expression library made from polyadenylated RNA of spinach seedlings. The sequence predicts a precursor polypeptide of 144 amino acids (Mr = 15.3 kDa), a mature protein of 95 residues (Mr = 10.4 kDa) that lacks methionine, histidine and cysteine, and a transit peptide of 49 residues (Mr = 4.9 kDa). The corresponding gene(s) is (are) designated psaH. The gene for subunit VII, psaC, has been located in the small single-copy region of the spinach plastid chromosome using a synthetic oligonucleotide and a heterologous hybridization probe. It is part of a polycistronic transcription unit that is constitutively expressed and processed. Putative processing products include a monocistronic RNA for psaC. The polypeptide chain of 18 (deduced) amino acids is highly conserved and strikingly resembles bacterial-type ferredoxins. It harbours cysteine residues that appear to be involved in the ligation of the two 4Fe4S centres A and B in photosystem I. None of the two subunits appears to be membrane-spanning, and subunit VI, as subunit VII, is located at the reducing (stromal) side of the reaction center. All available information on the major subunits of photosystem I from spinach has been combined into a (revised) topographic model. Evidence that the innermost - plastome-encoded - core of photosystem I represents an old bacterial heritage in present day chloroplasts is discussed.
authors.affiliation: Botanisches Institut der Ludwig-Maximilians-Universität, München, Federal Republic of Germany.
authors.forename: J
authors.initials: J
authors.lastname: Steppuhn
authors.forename: J
authors.initials: J
authors.lastname: Hermans
authors.forename: R
authors.initials: R
authors.lastname: Nechushtai
authors.forename: G S
authors.initials: GS
authors.lastname: Herrmann
authors.forename: R G
authors.initials: RG
authors.lastname: Herrmann
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D015152:Blotting, Northern; D002734:Chlorophyll / Q000235:genetics*; D003001:Cloning, Molecular; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000235:genetics*; D010957:Plasmids; D011498:Protein Precursors / Q000235:genetics*; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic; D014675:Vegetables / Q000235:genetics*
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D011498:Protein Precursors; D002734:Chlorophyll