title: Post-transcriptional and post-translational regulatory steps are crucial in controlling the appearance and stability of thylakoid polypeptides during the transition of etiolated tobacco seedlings to white light.
abstract: We have investigated the expression of nuclear-encoded chloroplast proteins that are not associated with chlorophyll (the lumenal 33-kDa and 23-kDa polypeptides of the oxygen-evolving system of photosystem II, plastocyanin and the Rieske Fe/S protein) by comparing mRNA-accumulation rates with those of the corresponding proteins during illumination of etiolated tobacco seedlings. Using subcellular fractionation, pulse/chase, Northern and Western techniques, we found that the biogenesis and stability of these proteins are regulated both translationally, as well as post-translationally, including the efficiency of mRNA uptake into polysomes, processes that operate between translation and assembly or monitor the status (soluble and membrane-attached) of a terminally processed polypeptide. Polypeptide synthesis is generally not limited by mRNA amounts. For instance, steady-state transcript levels may increase 10-fold during illumination, while those associated with polysomes increase only 2-3-fold without measurable influence on the rate of protein synthesis. The 23-kDa and Rieske polypeptides are predominantly membrane associated, but plastocyanin and the 33-kDa polypeptide are distributed among both soluble and membrane-associated protein fractions. Plastocyanin appears to be comparably stable in both forms. However, for the 33-kDa polypeptide, only the membrane-attached form is stable (> 8 h) and only this pool increases upon illumination. Its soluble form is rapidly degraded with a half-life of approximately 1 h under the chosen conditions. Our findings probably reflect part of a more general regulatory principle operating in the differentiation and maintenance of subcellular structure.
authors.affiliation: Botanisches Institut, Ludwig-Maximilians-Universität, München, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Palomares
authors.forename: R G
authors.initials: RG
authors.lastname: Herrmann
authors.forename: R
authors.initials: R
authors.lastname: Oelmüller
mesh_terms: D015152:Blotting, Northern; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D014450:Electron Transport Complex III; D005786:Gene Expression Regulation; D007506:Iron-Sulfur Proteins / Q000235:genetics; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000096:biosynthesis* / Q000235:genetics; D010947:Plants, Toxic; D010970:Plastocyanin / Q000235:genetics; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D014026:Nicotiana / Q000378:metabolism* / Q000648:ultrastructure; D014158:Transcription, Genetic
chemical_list: D007506:Iron-Sulfur Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D012333:RNA, Messenger; C037989:Rieske iron-sulfur protein; D010970:Plastocyanin; D014450:Electron Transport Complex III