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

J. Steppuhn, J. Hermann, R. Nechushtai, G. S. Herrmann, R. G. Herrmann*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Scopus citations

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 81 (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.

Original languageAmerican English
Pages (from-to)99-108
Number of pages10
JournalCurrent Genetics
Volume16
Issue number2
DOIs
StatePublished - Aug 1989

Keywords

  • Nucleotide sequence
  • Photosynthesis
  • Photosystem I
  • Spinach
  • Subunits VI and VII

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