Characterization of the LI818 polypeptide from the green unicellular alga Chlamydomonas reinhardtii.
The LI818 gene from Chlamydomonas encodes a polypeptide that is related to the chlorophyll a/b-binding proteins (CAB) of higher plants and green algae. However, despite this relatedness, LI818 gene expression is not coordinated with that of cab genes and is regulated differently by light, suggesting a different role for LI818 polypeptide. We show here that, in contrast to CAB polypeptides, LI818 polypeptide is not tightly embedded into the thylakoid membranes and is localized in stroma-exposed regions. Moreover, during chloroplast development, LI818 polypeptide accumulates before CAB polypeptides. We also show that the LI818 polypeptide forms with certain chlorophyll a/c-binding proteins (CAC) from the haptophyte Isochrysis galbana and the diatom Cyclotella cryptica a natural group that is distinct from those constituted by CAB, CAC and the chlorophyll a/a-binding proteins (CAA). Such an association suggests a very ancient origin for this group of polypeptides, which predates the division of the early photosynthetic eukaryotes into green (chlorophyte), red (rhodophyte) and brown (chromophyte) algae. Possible roles for the LI818 polypeptide are discussed.
Richard
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Department of Biochemistry, Faculty of Sciences and Engineering, Laval University, Québec, Canada.
Ouellet
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Guertin
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D020418:Algal Proteins; D000468:Alkalies / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D001965:Bromides / Q000494:pharmacology; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D005786:Gene Expression Regulation; D006863:Hydrogen-Ion Concentration; D007106:Immune Sera / Q000276:immunology; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D009154:Mutation; D017830:Octoxynol / Q000494:pharmacology; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D011817:Rabbits; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology; D017386:Sequence Homology, Amino Acid; D012965:Sodium Chloride / Q000494:pharmacology; D017670:Sodium Compounds / Q000494:pharmacology; D013861:Thiocyanates / Q000494:pharmacology; D020524:Thylakoids / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism
D020418:Algal Proteins; D000468:Alkalies; D001965:Bromides; D007106:Immune Sera; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins; D017670:Sodium Compounds; D013861:Thiocyanates; D012965:Sodium Chloride; C024553:sodium thiocyanate; D017830:Octoxynol; C027938:sodium bromide