title: Light regulates the rate of translation elongation of chloroplast reaction center protein D1.
abstract: Intact and lysed chloroplasts isolated from the day or night phase of seedling growth exhibit a higher rate of [35S]Met incorporation into the D1 protein in the light than in darkness. In the presence of the translation initiation inhibitor lincomycin, radiolabel incorporation remains unaffected for 7.5-10 min of the in vitro translation reaction, indicating that radiolabel incorporation is regulated by translation elongation. The rate of [35S]Met incorporation into D1-protein can be increased by addition of exogenous ATP to the in vitro translation reactions; however, ATP cannot replace light, and at physiological concentrations of stromal ATP (40 microM), the rate is at least 25-fold higher in the light than in darkness. This indicates that translation elongation is arrested in darkness. Separation of translation-elongation reactions into polysome-bound and membrane-integrated D1 proteins demonstrates that the rate of translation elongation is higher in the presence of light. In the light, less time is required to transiently radiolabel a D1 translation intermediate of about 17 kDa and to chase the translation intermediate into mature D1 protein. We propose that light regulates the enzymatic activity of the translation-elongation process in chloroplasts.
authors.affiliation: Department of Botany, University of Munich, München, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Edhofer
authors.forename: S K
authors.initials: SK
authors.lastname: Mühlbauer
authors.forename: L A
authors.initials: LA
authors.lastname: Eichacker
mesh_terms: D002736:Chloroplasts / Q000378:metabolism / Q000528:radiation effects*; D007700:Kinetics; D008027:Light; D008715:Methionine / Q000378:metabolism; D010441:Peptide Chain Elongation, Translational / Q000528:radiation effects*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D013462:Sulfur Radioisotopes
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D013462:Sulfur Radioisotopes; D008715:Methionine