title: Tab2 is a novel conserved RNA binding protein required for translation of the chloroplast psaB mRNA.
abstract: The chloroplast psaB mRNA encodes one of the reaction centre polypeptides of photosystem I. Protein pulse-labelling profiles indicate that the mutant strain of Chlamydomonas reinhardtii, F14, affected at the nuclear locus TAB2, is deficient in the translation of psaB mRNA and thus deficient in photosystem I activity. Genetic studies reveal that the target site for Tab2 is situated within the psaB 5'UTR. We have used genomic complementation to isolate the nuclear Tab2 gene. The deduced amino acid sequence of Tab2 (358 residues) displays 31-46% sequence identity with several orthologues found only in eukaryotic and prokaryotic organisms performing oxygenic photosynthesis. Directed mutagenesis indicates the importance of a highly conserved C-terminal tripeptide in Tab2 for normal psaB translation. The Tab2 protein is localized in the chloroplast stroma where it is associated with a high molecular mass protein complex containing the psaB mRNA. Gel mobility shift assays reveal a direct and specific interaction between Tab2 and the psaB 5'UTR. We propose that Tab2 plays a key role in the initial steps of PsaB translation and photosystem I assembly.
authors.affiliation: Department of Molecular Biology, University of Geneva, 30 Quai Ernest Ansermet 1211 Geneva 4, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Dauvillée
authors.forename: Otello
authors.initials: O
authors.lastname: Stampacchia
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Girard-Bascou
authors.forename: Jean-David
authors.initials: JD
authors.lastname: Rochaix
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism; D002736:Chloroplasts / Q000235:genetics*; D017124:Conserved Sequence; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010788:Photosynthesis / Q000235:genetics; D045331:Photosystem I Protein Complex / Q000235:genetics*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*; D018749:RNA, Plant / Q000235:genetics; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; D016601:RNA-Binding Proteins; C089909:photosystem I, psaB subunit