title: A cDNA clone from barley encoding the precursor from the photosystem I polypeptide PSI-G: sequence similarity to PSI-K.
abstract: A cDNA clone encoding the photosystem I subunit, PSI-G was isolated from barley using an oligonucleotide specifying a partial amino acid sequence from a 9 kDa polypeptide of barley photosystem I. The 724 bp sequence contains an open reading frame encoding a precursor polypeptide of 15,107 kDa. Import studies using the in vitro expressed barley PsaG cDNA clone demonstrate that PSI-G migrates with an apparent molecular mass of 9 kDa on SDS-polyacrylamide gels together with PSI-C (subunit-VII). The previous assignment of the gene product of PsaG from spinach as subunit V (Steppuhn J, Hermans J, Nechushtai R, Ljungberg U, Thümmler F, Lottspeich F, Herrmann RG, FEBS Lett 237: 218-224, 1988) needs to be re-examined. The expression of the psaG gene is light-induced similar to other barley photosystem I genes. A significant sequence similarity to PSI-K from Chlamydomonas reinhardtii was discovered when a gene database was searched with the barley PSI-G amino acid sequence. Extensive sequence similarity between the nuclear-encoded photosystem I subunits has not previously been found. The observed sequence similarity between PSI-G and PSI-K suggests a symmetric location of these subunits in the photosystem I complex. The hydropathy plot of the barley PSI-G polypeptide indicates two membrane-spanning regions which are also found at the corresponding locations in the PSI-K polypeptide. PSI-G and PSI-K probably have evolved from a gene duplication of an ancestral gene.
authors.affiliation: Department of Plant Biology, Royal Veterinary and Agricultural University, Frederiksberg C, Copenhagen, Denmark.
authors.forename: J S
authors.initials: JS
authors.lastname: Okkels
authors.forename: V S
authors.initials: VS
authors.lastname: Nielsen
authors.forename: H V
authors.initials: HV
authors.lastname: Scheller
authors.forename: B L
authors.initials: BL
authors.lastname: Møller
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D015152:Blotting, Northern; D003001:Cloning, Molecular; D005786:Gene Expression Regulation / Q000502:physiology*; D001467:Hordeum / Q000235:genetics*; D008027:Light; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000235:genetics*; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics*; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics*
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D011498:Protein Precursors