Chloroplast precursor proteins compete to form early import intermediates in isolated pea chloroplasts.
In order to ascertain whether there is one site for the import of precursor proteins into chloroplasts or whether different precursor proteins are imported via different import machineries, chloroplasts were incubated with large quantities of the precursor of the 33 kDa subunit of the oxygen-evolving complex (pOE33) or the precursor of the light-harvesting chlorophyll a/b-binding protein (pLHCP) and tested for their ability to import a wide range of other chloroplast precursor proteins. Both pOE33 and pLHCP competed for import into chloroplasts with precursors of the stromally-targeted small subunit of Rubisco (pSSu), ferredoxin NADP(+) reductase (pFNR) and porphobilinogen deaminase; the thylakoid membrane proteins LHCP and the Rieske iron-sulphur protein (pRieske protein); ferrochelatase and the gamma subunit of the ATP synthase (which are both associated with the thylakoid membrane); the thylakoid lumenal protein plastocyanin and the phosphate translocator, an integral membrane protein of the inner envelope. The concentrations of pOE33 or pLHCP required to cause half-maximal inhibition of import ranged between 0.2 and 4.9 microM. These results indicate that all of these proteins are imported into the chloroplast by a common import machinery. Incubation of chloroplasts with pOE33 inhibited the formation of early import intermediates of pSSu, pFNR and pRieske protein.
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Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK.
Gray
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JC
D025181:ATP Synthetase Complexes; D001667:Binding, Competitive; D060365:Chloroplast Proteins; D002736:Chloroplasts / Q000378:metabolism*; D014450:Electron Transport Complex III; D004586:Electrophoresis; D005287:Ferredoxin-NADP Reductase / Q000378:metabolism; D005294:Ferrochelatase / Q000378:metabolism; D015870:Gene Expression; D007506:Iron-Sulfur Proteins / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009097:Multienzyme Complexes / Q000378:metabolism; D018532:Pisum sativum / Q000378:metabolism*; D017856:Phosphotransferases (Phosphate Group Acceptor) / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000378:metabolism*; D010957:Plasmids; D010970:Plastocyanin / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism*; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D020524:Thylakoids
D060365:Chloroplast Proteins; D007506:Iron-Sulfur Proteins; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009097:Multienzyme Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D011498:Protein Precursors; C037989:Rieske iron-sulfur protein; C101484:import intermediate associated protein 100; C064388:oxygen-evolving complex, 33 kDa protein; D010970:Plastocyanin; D005287:Ferredoxin-NADP Reductase; D025181:ATP Synthetase Complexes; D017856:Phosphotransferases (Phosphate Group Acceptor); D012273:Ribulose-Bisphosphate Carboxylase; D005294:Ferrochelatase; D014450:Electron Transport Complex III