title: cis- and trans-Acting determinants for translation of psbD mRNA in Chlamydomonas reinhardtii.
abstract: Chloroplast translation is mediated by nucleus-encoded factors that interact with distinct cis-acting RNA elements. A U-rich sequence within the 5' untranslated region of the psbD mRNA has previously been shown to be required for its translation in Chlamydomonas reinhardtii. By using UV cross-linking assays, we have identified a 40-kDa RNA binding protein, which binds to the wild-type psbD leader, but is unable to recognize a nonfunctional leader mutant lacking the U-rich motif. RNA binding is restored in a chloroplast cis-acting suppressor. The functions of several site-directed psbD leader mutants were analyzed with transgenic C. reinhardtii chloroplasts and the in vitro RNA binding assay. A clear correlation between photosynthetic activity and the capability to bind RNA by the 40-kDa protein was observed. Furthermore, the data obtained suggest that the poly(U) region serves as a molecular spacer between two previously characterized cis-acting elements, which are involved in RNA stabilization and translation. RNA-protein complex formation depends on the nuclear Nac2 gene product that is part of a protein complex required for the stabilization of the psbD mRNA. The sedimentation properties of the 40-kDa RNA binding protein suggest that it interacts directly with this Nac2 complex and, as a result, links processes of chloroplast RNA metabolism and translation.
authors.affiliation: Lehrstuhl für Allgemeine und Molekulare Botanik, Ruhr-Universität Bochum, 44780 Bochum, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Ossenbühl
authors.forename: J
authors.initials: J
authors.lastname: Nickelsen
mesh_terms: D020121:5' Untranslated Regions; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics*; D002736:Chloroplasts / Q000378:metabolism; D007700:Kinetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics* / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase; D015533:Transcriptional Activation; D014466:Ultraviolet Rays
chemical_list: D020121:5' Untranslated Regions; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C070290:PsaD protein, cyanobacteria; D012333:RNA, Messenger; C101625:RbcL protein, plastid; D012273:Ribulose-Bisphosphate Carboxylase