Assembly of Photosynthetic Electron Transport Systems

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1. Structure and expression of genes the which encode P700-chlorophyll a protein complex---(1) A cDNA clone encoding the polypeptide from cucumber PSI (P700-chlorophyll a protein) complex that migrates with apparent molecular weight of 20 kDa on SDS-polyacrylamide gels has been isolated. The 907-bp sequence of this clone has been determined and contains one open reading frame that encodes a 22, 720-Da precursor polypeptide. The molecular weight of the mature polypeptide was predicted to be 17, 037-Da. The polypeptide was identified as the PsaD gene product. The biogenesis of this polypeptide was also studied. These results were published as a paper : Plant Cell Physiol. 31, 871-879, 1990.(2) Structural and functional aspects of cucumber PSI complexes have been studied. The PSI complex which contains eight polypeptides with apparent molecular masses of 65/63, 20, 19.5, 18.5, 17.5, 7.6, and 5.8 kDa, has been shown to catalyze the light-dependent transfer of electrons from plastocyanin to … More ferredoxin. It was found that the amount of 18.5 kDa-polypeptide is sensitive for the activity. The 18.5 kDa-polypeptide was identified as PsaF gene product and plastocyanin docking protein. A paper describing these results was submitted.(3) The N-terminal amino acid sequencing was carried out to characterize the genes of cucumber PSI complex that catalyzes the light-dependent transfer of electrons from plastocyanin to ferredoxin. A paper describing these results is in the press.2. Assembly of pigments-protein complexes during greening---The relationship between the accumulation of chlorophyll, heme and polypeptides during greening of cucumber cotyledons was studied. It was found that distribution of newly synthesized chlorophyll among apo-proteins is regulated by the relative rates of synthesis of chlorophyll a and apo-proteins as well as the differential affinities of the apo-proteins for chlorophyll a but not chlorophyll b. These results were published as a paper : Plant Cell Physiol. 31, 639-647, 1990.3. Expression of precursor plastocyanin in E. coli and reconstitution of mature plastocyanin---The precursor plastocyanin was expressed in E. coli and partially purified. The precursor plastocyanin was processed in vitro into the mature apo-plastocyanin. Copper atom was incorporated into the apo-protein the and resulting holo-protein exhibited the same activity for the electron transfer with the native purified plastocyanin. A paper describing these results is in the press. Less